You mean fluffwise? Well basicly all the grey knights are psychers. As the nemesis force weapon they carry guide their psychic enery to enhance their strenghts.
By rules:: Baiscly anything that can take psychic powers. Things like, grandmasters inquisitors brother captains. These are able to purchase psychic powers and thus count as psychers.
Cherubal ain't death. Inquisitor Eisonhorn had captured him, and later used him as his own deamonhost. It can all be read in the book Eisenhorn. He was puritan at first, and locked Cherubal away. Yet when mister-no-good stood face to face with a chaos warhound titan he couldn't do anything else except summoning Cherubal as a unbound deamonhost and make him destroy the Titan. Since that point he started to see the potential.
There are no records of a being such as cherubal in imperial database at the end of the book, except the part about Quickos or something, which made Cherubal, and his brother. Its a good book IMO and you should read it.
