Im currently trying this at 61 with 3xLocks and 2xDruids. ITS A MESS. Im sure it can be done, but its a complete cluster %^#! if you've come from a sham team.

Pros: -When talented correctly u can often summon more pets as they die.
- Many fun pets such as Felguard and Infernal(a must if u choose this team!).
- Dots are very mana friendly, combined with shadow bolt spamming its alot of dps.
-Lots of tricky warlock spells such a shatter, healthstone's and weapon enchant stones

Cons: -Lots to control, 3dps 2heal and 3 pets, its harder than it looks!
-The pets often lose aggro if u even go half-out on dps
-Your pets will pull everything if your not carfull! Prepare for the wipes!
-If they fail to aoe aggro correctly your heals will pull the mobs, and good luck getting them off...
-very very very slow way to do an instance
- The most important con to consider = the warlock class is IMO THE MOST COMPLICATED class to play. Thus multiboxing it will give u kidney stones.

Perhaps someone else has more comforting information, I am a little biased from my last few Hellfire instance's.
Good luck with whatever u choose