Currently, OOA seems immune to all spells. On live, he's slowable, lifetap lands easily and hes stunnable. He's much more resistant to fire/ice/poison/disease but his MR is left pretty low
On here, pet lifetap doesnt land which means he has really high resistance to magic(if not immune).
http://eqbeastiary.allakhazam.com/search.html?id=4639
Search for slow in there and youll have multiple entries about it.