Last run I did the uggs spawned and went straight for the healer even after I AOE taunted (Shadow Tank or Guardian Tank).
Taunting doesn't work you have to quickly aoe damage them and make sure your dps don't use thier aoe and pull them off you.
It's pretty simple:
1. Tank pulls boss
2. Tank saves instant aoe attack for when adds spawn and pulls them into the flamethrower
3. DPS quickly burn down the boss and only the boss
4. DPS refrain from using AOE
5. Healer heals