The Spirit Realm

As far as I am aware, all of OMM's ae's are hatelist based, but also have range limits. His hatelist is constantly changing, because everytime he gets "afflicted by his own magic" he memblurs, meaning the mask clickers have to retag to get back on his hatelist in order to be valid targets for his gaze. Its not totally a downside however, if you accidentally get on his hatelist as one of the 'dog kill team' or emergency curers, once you get cured and after the next successful mask click you are safe again. Another very big advantage of the memblur is it lasts for quite a long time, for the entire period that he is prone and not fighting back nothing you do can add you to his hatelist, its only when he becomes active again that he starts addign people to his hatelist. This makes while he's prone a great time to cure everyone and cast group heals etc.
OMM's difficulty dropped by gigantic amounts with the level increase, his ae's are very resistable now, so much so that on my last omm while being the tank group bard furiously playing every ac song on them I have, i didn't get silenced once for the entire duration of the fight. (625 all resists due to psalm of veeshan).
If your tanks and clerics can handle his dps output, and your rangers are fast to react (or the smart ones are casting at just the right time pre-emptively) in the event of a missed click it should be doable. Strategy is definitely your biggest advantage on that fight, much moreso than gear. Ream of Insanity on the progression server beat him after only 2 months in anguish.