As regards the identity of the so-called aliens, I would have say that the evidence leans heavily in the direction of their being demons, unclean spirits (if there's a difference), or something very similar.
IIRC, David Jacobs and Budd Hopkins (and possibly John Mack) had some cases in which experiencers said there was a creature present in their abductions that was lurking in the background and this creature "appeared" to be a kind of mantis-like being. Several described a similar being sitting on a throne-like captain's chair and wearing a dark hooded garment.
As is often said, this may be a projection on the part of the experiencers or it may have been something projected onto the experiencers by their abductors.
Demons have no physical body so they seek a host, as illustrated with the scene where Jesus casts ‘legion’ out of the man and into swine.