Alienhunters
Ordo Xenos is their official title. These guys hunt aliens (you'd never have guessed that) - the kind that will either eat you alive, beat you to death or both. Some are also prone to rape and torture.
They don't get bitchin' hats or warp-immune, hymn-murmuring, deamon-churning dudes but instead they get a guy in a floating chair and someone who can't smile.