In fact, even non-citizen residents have to register (except those who are on non-immigrant visas), and can be drafted if the draft is reactivated.

This includes undocumented immigrants, regardless of whether they ever had a visa or not.

oh wow, I didn't even know that (the last part).

I've always thought that if a non-citizen is inducted into the armed forces in any way they should immediately be eligible for citizenship. As I understand it, there's still a relatively complex process they have to navigate to get that done.