Are gods aliens in the Marvel Universe?
They are aliens who are so powerful and have such amazing technology that less developed species, such as humans from Earth, think they are Gods. But they aren't really Gods, not in the sense of personifications of certain aspects of the Universe.
There are real God, such as Lady Death, Infinity, Eternity, Entropy, The Living Tribunal, Galactus, Dormammu and of course The One-Above-All.
This is highly dependent upon your definitions of "gods" and "aliens".
If by "god" you mean beings that are especially powerful and immortal and by "aliens" you mean beings that aren't from earth, then the answer is yes. The most powerful beings in the Marvel Universe are not from earth. A great example would be the most powerful of the Asgardians, which are so much stronger, longer lived, and more advanced than humans that they spawned religions on earth.
Other god-like beings in the MCU include celestials like Ego, who are definitely not from Earth and are therefore aliens by some definitions. The MCU, however, has not explained these things in great detail just yet. So at best, you can guess at their true natures by taking a look at the comics.
...by asking it like this... you point out the real world GOD is not from this world. He would be an alien. So would angels as they are "not of this world"
Gaia is would technically be of this world since she does if it dies, she's put that much of herself into it. So I would go by that definition.
Odin and Zeus rule over earth but are not dependant on it. So that makes them aliens? Zeus's dad is for sure and immigrant. So Zeus is 2nd generation and Hercules 3rd?
And clearly Klu'rt and his mate are aliens being gods of aliens.
and then there are Pathers that ARE earthbound. But they are usually lesser in power.
If your referring to such beings as Odin, Thor, Zeus, and so on, they are gods with a small "g", but the people of Earth that interact with them on a daily basis see them as an advanced alien race. I'm going to leave it at that because delving too deep into it here would get into a theocratic discussion that would take up too much time.