Carefull, they could be all the insergents that they are letting out of prison re-joining so they can get a uniform.
Or maybe the Sunnis are just now frealizing the obvious: that they will never be top dog again, and that if they want a solid piece of the action, they had better play the game the way the Kurds have. Carve out a niche. It is quite possible that the territory they control will be a good bargaing chip, even if it doesn’t (although it probably DOES) have oil reserves buried. Anyway, so long as they are getting paid by the central government to maintain security, that is a left-handed way to get a share of the oil revenue.