The relictors are often picked by radicals (for obvious reasons), whilst I don't know of any others that have long standing pacts with the inquisitation. Though there's nothing stopping you creating your own chapter to go with them. Something like Black Templars (though you can't use their rules in the DH codex)would fit the theme nicely. Plus I've just thought you can't field both marines and Grey Knights in a DH force, but you can field GKs as allies to a marine force (confused? why one way and not the other is beyond me...). The long and short of it is its probably easier to create your own.