Second, very thought out response thank you.
Given that your scenario (in my experience) happens more times than not and I've done a LOT of PUGs (both as party member and (in fewer cases) leading), it's been my experience that the better party leaders ask before they actually start the run, what backup skills the party has and states that we may have to use those skills as needed (For Rifts I would think our other roles (if any) would fall into that category) for the good of the group. The really GREAT leaders (of which I must confess I am NOT) remember that discussion and then directs the people with those skills to use them.
So I guess I'm saying that more communication at the beginning would make the need for threads like this to be a lot less.
I hope this rather contorted post makes some kind of sense.