Ayahuasca has some unusual characteristics which make “any” kind of hallucination possible.
(1) It is usually taken in groups and there are shared hallucinations.
(2) McKenna and others have argued that these hallucinations do not provide a reliable source of “new” data (as opposed to DMT and psilocybin).
(3) The reason is that ayahuasca taps into memories of the group and/or historical memories of previous takers of ayahuasca.
(4) Those group (or individual) memories are often of Jungian archtypes—and at this point in human history gray aliens fall into that category (along with flying saucers of course). The grays would be symbolic of the “other” or demons for folks raised as Christians. In the case of Amazonian tribes the archtype is most likely to be wild animals (like the jaguar) while westerners may be see flying saucers or gray aliens if they tap into western memory or wild animals if they tap into the Amazonian group (current or historical) memory.
(5) Ayahuasca can be thought of as a “historical” drug—so anything in human history can be part of a vision.
DMT and Psilocybin are where the visions are of the impossible, the unimagined, or possible high tech futures.
Isn't DMT the main active ingredient in ayahuasca (the other being an MAOI that prevents the DMT from being metabolized in the gut)?