Mormons do indeed believe that god’s creation extends to other planets.
Problem being that the assumption is that those inhabitants of other worlds are just like us, made in the image of god.
So, considering the extreme unlikelihood of an alien species looking remotely like us, I think the arrival of extraterrestrial beings radically different in appearance yet apparently superior in intelligence would create a conundrum for religions that believe in an anthropomorphic god.
Since, in Christian religion, the belief that we are special above other animals on earth is based not on our superior intelligence, but the belief that we’re created in the image of god and, as his children, are the purpose for the earth’s creation, it would probably be easier for those religions to explain the new arrivals as being demons, angels, or just highly intelligent animals, but not god’s children.
You might get some sects referring to our new visitors as “seraphim” or other celestial creatures mentioned in the bible, as a way to show that they can still be made to fit into the biblical narrative.
As we learned more about our new neighbors and the differences in their culture, civilization, thinking, and morality, it would probably become increasingly difficult to explain their existence within current religious doctrine. The more you know, the harder it is to keep believing what you thought you knew.