The website doesn't use the terms “Nordic Aliens” or for that matter “Aliens”, because it doesn't have anything to do with the original story.
But the term does have its own position on the website, assuming of course it originates from 'George Adamski' and 'Howard Menger' and not 'David J. Skal' - under Other Contactees#Frauds.
Thoughts and opinions
The Scandinavian Peninsula became ice-free around 11,000 BCE, i.e. at the end of the last ice age, see Scandinavian prehistory (Wikipedia), thus the “Germanic Aliens” would make for more sense - but with these fantasy authors, 'sense' doesn't necessarily unconditionally fit into what they're doing. The Plejaren Federation incidentally are multicultural i.e. containing several cultural or ethnic groups, so it wouldn't work even if it wasn't made up; would be questionable even if it originated from said extraterrestrial civilisation. The term "Alien" is not used, because on the one hand, the Plejaren in this special case know more about us than we know about ourselves, see ageing, i.e. the definition of 'alien' doesn't work. While on the other hand we don't use the term "Alien" because it quickly becomes offensive, xenophobic and alienating, which fundamentally goes against the good valueful principles of FIGU in their basic form. Even were the 'being', see Humanoid lifeforms in the known universe, assuming there was a 'being', was unfamiliar and completely foreign to us, the term "Alien" wouldn't be an appropriate way of referring, because it is too hostile, hateful, anti-, and fearful, for what is essentially another living being, it would be wrong.
Had you of already read the actual story in its original form you would know space conquest is the exception not the rule and an aspect of what the Plejaren Federation are doing, is to 'ward off' any others from Earth, so that we may be left in peace to evolve normally - if you want to call it normal, see ageing.
The website doesn't use these terms because it doesn't have anything to do with the original story by FIGU.