There are games out there with melee healers. I'm fairly sure half the healer subclasses for Cleric in Rift were melee or a ranged/melee hybrid (admittedly I mostly played Mage, so I only vaguely remember) and they were fine. The only point of friction would be high end content where a melee spot would have to be given up to a healer, which DPS would whine about.
