Based on what Ive been testing, yes It works. I never get heal agro issues when I put maddening defense down with my Guardian. With my DPS tank types, they do have this problem ( heal agro ). For my DPS tank types I have to switch targets in order to keep the multiple mobs off my healer. I test this in a duo situation BTW. With enough damage dealers or healers to spread the agro out, it affects the tests.
Ive never noticed that maddening defense triggering uses mana. Im not saying it doesn't. I just never noitced that. Thanks for the tip ) I will have to say that against power drain type mobs the skill does seem to keep working. The beasties in Nek 2 for example. They hit hard and have plenty of hit points. Maddening Defense prevents healer agro for sure and everytime. I have had my Dirge steal agro at times like this. I have no mana to enhance my damage or taunts so over time he takes agro away. This is where maddening defense fails since it only works when your getting hit.