I got this ring last night with a 40th Druid. Arynduil gave perfect instructions on where to find Hamed Grarr. I think I was the first to get to him right after a patch, so he was up when I got there. I killed him using the following tactic: Entwining Roots, Drones of Doom and then three Firestrikes. The other mobs in the room were healing like crazy, but didn't attack me. This tactic out-damaged their heals.
Ok, so he spawns 3 times in a row for me, but drops the Kerran Headband and some small loot each time. His spawn time is 20 minutes, almost to the second. Then his PH spawns once, which is "a kerran ahmad shaman". Hamed spawns right after that again, but still only drops the headband. After this, I don't see Hamed Grarr for 15, yes 15!, spawns. Then Hamed spawns and drops the ring. When he did break Root and hit me, it was in the mid-30s, max.
Good luck. Killing Hamed isn't that tough if you can outdamage the healing of the others. If you happen to be in-range of the other 4 mobs in the room, it's going to be tough.
Hope this helps.