Yeah, they didn't have much involvement in the Heresy after essentially touching it off.

Edit: As to the question regarding what sort of operations...Blackshield Marauder bands did tend to strike fast and then get off planet, so they probably will function a lot like a Deathwatch Kill-Team would in later eras. On the other hand, some of them will have the expertise to coordinate larger battles due to experience in the Great Crusade. I think we can play it by ear, but I feel like the way to go would be to have them, if necessary, commandeer (at bolter-point if necessary) the gear on the ground they need to do the job.

I imagine quite a few of them will be looking to atone and willing to undertake risky missions. That was always the role of the Legion Astartes but these guys are probably more eager for it than most and are not considering the preservation of their forces anymore.