I have a similar group make up. 3 Affliction Warlocks, Holy Priest and I'm using a Paladin. A blind retarded chimp could use a paladin for a MB tank. I don't see any negatives at all for using a Paladin, esecially with a mxed group and a first time multibox group. (I like the 3 locks btw, DoTs can really melt down mobs and really no sudden crits that gets a mob looking away from the tank.)