The most experienced person should be running the group, regardless of role. If that happens to be one of the DPS filth, then that's how it's going to be. I've walked first-time tanks through experts by calling pull locations and breakpoints, and it went just as well as if I had left a pro tank to do his thing.
Also, some DPS (read: DRG) can back up a weak/undergeared tank by splitting up incoming damage. It's more healer load to have two targets to monitor, but there's considerably lower risk of everyone dying terribly from the tank blowing up under a trash pull.