I have access to 8 level 100 characters, I used all 8 yesterday to try for Orumo. 4 on main account, 3 on second account, and 1 on my daughters account. 0 for 8 tries.
The custom party finder is a big help to getting parties for this. I searched by the word "Orumo" and often found groups going. I even started one of my own, that was pretty cool. I had enough people to start it in about 10 minutes, even shut it down because people were still adding when we were getting ready to engage.
You need at least 5 people to start it and he doesn't seem overly hard he has some beam type abilities that hurt a lot, but if you stay out of the way it was pretty easy.
The only bummer is that you need a certain daily apexis crystals mission (I believe it's Heart of Shattrath) to be up and it seems to be uncommon to pop. Wish it was as common as the Pit mission.