BSD on the RT was "AOS" - academic operating system, if I recall.

I don't think we ever saw AIX on the RT (at MIT Project Athena, which
had probably the second largest collection of RT's, the largest being
of course CMU, who also ran AOS) though we did have AIX on PS2 (386/16
and /25 boxes) which mostly served as a "disproof of concept" :-) at
about the same time or maybe a little later.  So it may have existed
(and I do remember talk about the AOS/AIX schizophrenia within IBM at
the time, though I think it was also cross platform) but it didn't see
much of the world...