I mean this in an entirely practical and nonpolitical way. Do they need to get a visa to stay in the US? Do they get a visa as human for human looking ones or with a human disguise for the non human looking ones? Does the US government in the US have some sort of policy regarding issuing visas to aliens? By aliens, I mean actual ETs
Again not trying to be political, just kinda curious
In the MU, I'm pretty sure most aliens are there in disguise. Or at least not publicly. Some have integrated (or been integrated) well enough into human society that they're effectively citizens of wherever they live regardless of their secret or public extraterrestrial status (Hulkling and Karolina Dean for instance). Others spend all their time being crazy superheroes/villains, so they don't seem to spend much time worrying about legislation and such (Noh-Varr).
The technical legal approach to being an alien on Earth would probably involve going through SWORD. My guess would be there's some sort of registration process; whether it involves the US specifically or just SWORD as an international agency, no clue. The details of how it works are pretty much unknown; you don't see many instances of aliens trying to petition for legal status on-panel.