It's a silly idea. Why would they bother?
In any case, there's no evidence for it. A person might as well believe that dragons disguised as squirrels secretly rule the world. There's no less evidence for that.
There might or might not be people of other species elsewhere in the universe. We've no evidence of it, but it is a possibility. We know that the possibility of people existing is not zero and we know that the universe is a very big place. It might, for example, contain dragons that could disguise themselves as squirrels.
It's possible, though far less likely because of the size of the universe, that one or more species of people from elsewhere (if there are any) are aware of the existence of humanity.
But if they had such spectacularly advanced technology that they could come here, why would they be ruling from behind the curtain in a way indistinguishable from them doing nothing at all?
Besides, everyone knows that the world is run by the council of faeries and werewolves.