Snareable/rootable, and summons. I was able to take him with group equiped war/dru box ( + 2 clr mercs, tier 3 ). Focused on dps with dru, dotting like crazy, shield tanked with war with crystallos chromasteel gear. only raid item on war was epic 2.0 ( groupable now ).
I snare parked the spiders and frogs away from him ( snare/evac/gate back ) so no clearing necessary.
I test pulled him today and found that the thralls will not assist him however the spiders and frogs will (just as the spider and frogs will not assist the thralls unless you have the quest to free them). If you find that he's spawned next to either of those, make sure you either fight him on location or kill locals then engage. I can tank him on my rogue (magelo in sig). I had gallantry, unity, fabled earth illusion clicky (85000 mitigation or some such), and lithe running. My mage had a j5 lvl 84 merc and I had a j5 lvl 85 merc healing. I did have my locustlure proc at about 70% of his life but I lost the fight because some folks decided it was a good idea to jump my camp to do their quest while I was waiting on respawn of the thralls and hopefully him. I gave them plenty of warning but they did not listen (well one did) and they all died after a frog jumped my mage and I. They didn't realize Shem was kos to all.