Nope, those aliens have always existed, that's how they created the universe because they are outside of it.
If those aliens create the universe and exist outside of space and time, then they are by definition, "God".
So a person believes in aliens who created this world would be a theist, not an atheist.
No, actually not at all. God is first of all an invented word but never mind that, the broad definition of god is a creator/being/spirit that created the universe, however that's all singular, it's not defined as a few beings working together to create the universe which could be just as possible, wouldn't you say?