I don't know. We have a few groups around here. I have seen them while out on group rides, we wave, they wave. No probelm.
I hang out with a riding club (rc), who just had a spring dance/chili cook off, there were a few people from MCs sporting different colors. Again no problem. They are like anyone else treat them fine and they treat you fine. But ****** them off and instead of muttering under their breath and whining about it on the net. They will take care of the problem then and there.
Oh and most of the MC guys who have seen my bike got a real kick out it.