I don't mind if someone else ends up pulling because of CC reasons or perhaps to do a better LoS pull. If I am in a pug and the tank doesn't seem to mind the other person pulling first (usually NOT the case, but it does rarely happen) then I just deal with it. Of course if they end up dying because they take too much damage or the group complains I have to drink more often than normal because I'm spam healing, then I'll inform them of the easiest solution to that problem. I haven't had a ton of trouble with it but the issue has occurred a few times since I've been playing. If I'm not busting my back keeping them alive, I just deal with it. But if it's causing added stress because dps is pulling and the tank isn't as geared, then we have problems.
I think it also depends on if the tank is bad or not. If the tank sucks and a dps i pulling because of that, heal the dps. If the tank is slow as hell, let the dps pull and heal them, if its pre-80 dungeon let the dps pull and who cares who tanks. Hell i've tanked and healed on my priest in pre-cata dungeons.