I'm sure it's regional, but my guess being that what your saying is probably much more prevalent these days than not.
Our state guard here in Virginia used to have an MP unit that was trained and equipped for crowd and riot control, though I don't know how effectively so. It's a dying organization with few members left, so that went away a few years ago with a reorganization. Frankly the whole damn thing should probably be dissolved and assimilated by their members' respective county CERT or MRC given the overlapping/competing missions, with CERT and MRC have a much more appropriate expectations for the members that doesn't have people running around in fatigues referring to themselves by military rank.