Yes, poes are ghosts, spirits, if you prefer.
And it's true that some people refer to aliens as "them/they", but, lots of people do that concerning ghosts/spirits as well.
So still in a draw, here
Romani never uses the word "aliens".
She only refers to them as "them" or "they".
Even though the method they use to abduct cows is very alien-ish, we can assume that they are poes.