Maybe they follow some Orc deity of outcast, which ironically is what the Orc's in Elder Scroll follow.

Though since we're taking points from WH40k of all things, I always liked the honor bound system that the Orsinium followed. It would make a band of outcast joining together and staying united more feasible if they had some kind of tradition of honor. Which fits orcs to a tie as most warrior societies have some kind of honor system. In any case I like the elite group idea. 

"If history is to have a voice, Let it be known that the Orc's have sought for nothing more...then a good fight."