Unlike the other encounters in Dragon Soul, Warlord Zon'ozz only requires a single tank. For cooldown purposes, it is possible to bring in a second tank; however, there isn't too much of a need to do so. Per usual, you will want to have around five to six healers. Switch your off tank for an additional healer if you feel that would help. Your DPS should be a solid mix of both ranged and melee; there does need to be a solid balance of both. Healers should be split among the DPS, with tank healers staying with the melee.
Zon'ozz doesn't have all that many abilities, but he's still a hands-on encounter. Most of your time will be spent watching the Void of Unmaking and bouncing it back and forth. Healers will focus more on clearing away Disrupting Shadows. For once, tanks probably have the easiest time on this encounter, only really having to watch out for a single ability that occurs about once per phase or so.