First let me give you a some background information on the Nordics & the Greys.  According to the article at Grey Aliens Signed Treaty With Eisenhower In 1954, After U.S. Government Rejected Overtures From Nordic Or Pleiadian Aliens, Say Conspiracy Theorists the Nordics wanted to make an agreement with Eisenhower and "demanded nuclear disarmament and warned that humanity was on a path to self-destruction. They proposed instead to help humans to develop along a peaceful path to spiritual fulfillment.  Because the primary interest of the U.S. government at the time was signing a treaty that gives access to advanced alien technology, the Eisenhower administration rejected the overtures from the first alien group — the Nordic aliens — during the First Contact meeting at the Edwards Air Base and agreed to sign a treaty with the second group — the Greys — during a subsequent meeting at the Holloman Air Force Base in New Mexico in 1954."

"Details of the agreement with the Greys leaked by whistle-blowers include non-interference in human affairs in exchange for accommodation on Earth under conditions of secrecy. In return, they would furnish the U.S. government with advanced technology to help the country to stay ahead of enemy nations. The Greys also agreed they would not approach any other nation to make a treaty. The Greys were housed in an underground facility in Dulce where Phil Schneider claimed he encountered them while working as a geological engineer employed by a private company contracted to build underground bases for the Greys. Part of the treaty agreement allowed the Greys to abduct a very limited number of humans for medical research and experiments. But the Greys proved untrustworthy and violated the agreement on abductions. Part of the treaty agreement allowed the Greys to abduct a very limited number of humans for medical research and experiments. But the Greys proved untrustworthy and violated the agreement on abductions." 

FULL STORY at above link.

As to how the fallen angels can be compared to the Nordics, the author of the article The Nordics: Not Tall Whites, Not Benevolent, Not What You Think describes them as "more human-like than any other group. Often described as luminous or radiant.  Deeply connected to antiquity. Associated with warnings, interventions, and “teachings” 

they appear in both physical and non-physical form."

As you know angels can appear to look like humans as show in Genesis 19:1-11 when they appeared to Lot & the men in the city of Sodom who thought the angels were men as the men from Sodom wanted to have sex with them. As for the Nordics being luminous or radiant, the angel at Jesus' tomb (Matt. 28:2-3) his countenance was like lightening, and his raiment as white as snow.  And the angel's face in Dan. 10:6 was as the appearance of lightning and his eyes as lamps of fire. Also Satan the fallen angel can appear as an angel of light because 2 Corin. 11:14 says, "And no marvel; for Satan himself is transformed into an angel of light.  So even a fallen angel like Satan can appear radiant like the Nordics.  Also the fact the Nordics can "appear in both physical and non-physical form" like the angels and the fallen angels leads me to believe that the Nordics may very well be fallen angels as part of the great deception to men on Earth. And if they aren't fallen angels, they very well could be hybrids made by Satan and his fallen angels along with hybrids like the Greys, Reptilians & Insectoids by combining the DNA of mankind with other creatures' DNA to come up with these weird looking creatures. It also may be possible for fallen angels to also shapeshift to look like a Grey, an Insectoid or a Reptilian because Satan, the fallen angel, shapeshifted to look like a talking serpent in the garden of Eden, and a serpent is a reptile.

This article The Vril Society Secret: Nordics, Nazi UFOs, Body-Snatching, and the Hidden System of Power by the same author will tell you how the Nordics are tied to the Reptilians, the Illuminati & the occult. Below are some excerpts from the article, but please read the entire article to understand more about it.

"The Nordics and Vril lizards are not described as one single species or even as a formal partnership. Instead, they converge through the same human networks. On the “upper” side, Maria Orsic and the Vril Society are stated to have received Aldebaran transmissions from tall, Nordic-type beings, including scripts and diagrams used to design early saucer craft. On the “lower” side are the Vril lizards - small subterranean reptiles with a proboscis that enters through the eye to take over human brains that were being used by Nazis - and later Illuminati elites to create droned human hosts in positions of power. The same occult-political ecosystem links both: Nazi and postwar power structures sit in the middle, taking information and technology from the Aldebaran Nordics while employing Vril lizards as a biological enforcement tool behind the scenes."

"Vril lizards - the subterranean reptilian species linked to the inner-Earth pact - are parasites with a biological ability to invade a human body through a proboscis that injects fluid into the eye, takes over the brain, and kills the original consciousness. The result is a “drone” or “host”: a body that appears normal, remembers its life, but is now run by something else. The Illuminati use Vril body-snatching (“droning”) to systematically replace key people with hosts loyal to the underground agenda. Government, banking, media, Hollywood, law enforcement - anywhere leverage is needed, a human can be removed and a Vril-run host installed, with no obvious external change."

There are two main pathways to power:

"The Host Path: A human is droned - bodysnatched by a Vril parasite and turned into a host.The host retains memories, skills, voice, and habits, but now operates with a cold, predatory psychology aligned with the pact. These hosts are strategically placed or elevated: they move quickly through the ranks because they are useful, compliant, and guided by nonhuman intelligence that understands leverage."

The Pact Path:A human voluntarily aligns with the Illuminati structure that manages Vril access. In exchange for loyalty (and in some cases the sacrifice of others), they receive protection, opportunities, and energetic amplification. Doors open. Algorithms lean in their favor. Contracts fall into place." FULL STORY at above link.

(MY COMMENT -The Pact Path reminds mean of the Satanic rituals that were carried out far below the Vatican where children were sacrificed and their flesh eaten along with their blood being drank by the participants.  This was order to gain power, and at the time of the Satanic ritual an entity (demon or fallen angel) could enter into a participant.)

Below are some excerpts from another article Nordic Aliens: The Truth Behind the Extraterrestrial Beings | Gaia

"Nordic aliens, also known as Tall Whites, Pleiadians, Venusians, and Space Brothers, are often regarded as angelic beings who have appeared in humanity’s stories since ancient times. Many believe these luminous visitors were revered as gods, teachers, or messengers of light, guiding early civilizations and shaping spiritual traditions around the world." 

"Their influence is said to echo through ancient myths, sacred texts, and folklore that describe radiant beings descending from the heavens to share wisdom and technology with humankind, such as the following: 

• Some researchers suggest these extraterrestrial beings may have visited ancient Mesopotamia, influencing Sumerian culture with their advanced knowledge.
• Ancient Egypt’s advanced astronomical and engineering skills, along with depictions of tall, fair-skinned beings, hint at possible Nordic alien influence.
• Ancient Greek mythology’s descriptions of gods and demigods resemble the physical traits attributed to these beings, further suggesting early encounters.
• Viking folklore and Norse mythology describe gods with characteristics akin to those of Nordic aliens, suggesting visits to ancient Scandinavia.
• Indigenous cultures in the Americas, such as the Hopi tribe, have prophecies of “True White Brothers,” while Mesoamerican legends speak of white-skinned gods.
• Ancient Indian texts describe fair-skinned deities and advanced flying machines, potentially linked to Nordic aliens.

(MY COMMENT - In my opinion the Nordics sound like the fallen angels, and the fallen angels could have given the Sumerians, Egyptians and other civilizations advanced technology and would have been worshipped as gods. As for the gods and demigods of Greece, the fallen angels could have been the gods, and their children, the giants, could have been the demigods. It sounds logical because the demigods had one divine parent that was immortal and one human parent.)