"Are you restricted to a narrow mind?
Is your heart limited, your view confined?
Scared by some magic symbols, some new word,
you have to hear what you've always heard?"
- Goethe's Faust.
The most important part for the aliens that should be included as part of the White Wolf system is the fact that they do not have magic. In fact for the purpose of the game the aliens don't believe in magic. That is not to say that they refuse to believe in it but rather that it is something they have never encountered before in any sense. Mankind is unique in the universe for having created through their own wishes and desires the metaphysics of the word around them in the World of Darkness. Aliens have no technocracy or traditions or clans or breeds. They are unified races, working against other worlds rather than against their own. One of the main elements of the World of Darkness that you cannot trust anything, let alone your reality. This is something that the greys add to but don't adhere to.
The alien mindset comes from a scientocracy. Science being the study of nature and technology being the setting of boundaries of nature. The aliens have developed tools to study all forms of nature but they do not regard any of their developments to be technology as mankind would. To them it's all perfectly natural, which is why they have such complete mastery over it all. They feel that most of the technology on earth today is beneath them, simplistic structures that are lucky to be able to do the job they have been designed to do. This is why the Technocracy refuses to believe in them and those Void Engineers who do encounter them believe that they are merely more powerful chantries, magicians from beyond whose very experiments and reality deviancy has resulted in their altered forms. The fact that they themselves have created LERMU's that bear an unwitting resemblance to the actual Grays makes for an interesting study (especially as the Grays themselves consider their bodies to be nothing more than physical shells). But it remains that the Void Engineers study via Umbral space, not true space.
Greys are, in effect, the physical embodiment of the universe. The order that comes from the chaos. They do not try to structure their reality and, rather than fight against it, they go with the reality of the situation.
Greys have no concept of using will to make something work. They do believe in the power of the mind, but souls and willpower have never been brought into their mind-set before. These are alien concepts to them, and are likely to be treated as interesting theories, if explained. They are so confident in their science that they will be able to explain it eventually.
However, due to their nature as scientists nothing is impossible, just highly improbable. This means during the course of the game that if they encounter something that would normally scare the wits out of anyone, they react with suitable regard for their own safety but that's about it. Paradox spirits do not affect any Mages around them as paradox can not exist around such open minds. Creatures of the Night are treated as any other people (that is with not much respect) and any attempts to use powers will result in indifference from the Greys as they will come to study and learn all about it in due time.
In closing the best way for me to describe the difference in backgrounds from us and them is to look at the clouds. When we look at clouds we see a myriad of forms and shapes being made out of the lines made as they are pushed through the air by the breeze. Aliens see clouds. Or to put it another way they see moisture condensation in a semi-gaseous form. Never a dragon.