Yes, I'll always put ambient mics out when I'm mixing monitors for IEM. Usually a small condenser mic at each side of stage, firing up in to the room (you often see them pointed straight at the crowd, but I find you get too much "front row chatting" that way). Some people like them subtly in the mix, most likely them just pushed up in between songs so you can get the vibe of the crowd that you can't hear naturally because of the isolation.      Yep, they're in the outer fringes