I was healing a dungeon (Old Hillsbrad Foothills to be precise) as a resto shaman. There was a fury warrior in the dungeon that was PvP-flagged (They said they had warmode on.) and I was completely unable to heal them. I myself did not have warmode on, and I know the tank did not either. I did not see anyone else in the dungeon that was PvP-flagged, I could heal the rest of the group as normal.
Oh, adding that I was in BC Chromie Time. Not sure if that’s obvious or helpful, but wanted to add that in.