I'd say they are, but they're also too far removed from any kind other kind of psychic that it makes sense to just consider them as not.

Nope, that was a **** up by Ian Watson In the Dracco books. Everywhere else states otherwise.
Technically no. The Inquisition trilogy was written around 25 years ago, way before any other 40k novel. The inconsistencies in those books are more because there was nothing to be consistent with when they were written.