If you've done the raid, the orcs do not spawn in the same place. In the group version they spawn one small level right above the boss. There's two or three spawn points, and if you run up the little ramp that Danela roots herself near, you'll see them.
I'm not sure if this is just bugged, or it's intended this way, but when she goes into Terror form and orc adds start spawning, they don't seem to stop. They may stop after you drop the first boulder, but after doing this mission twice, they did not stop after the second terror form. We had luckily saved our burns for this, but we had 8 or 9 of them throwing barrels by the end after we had killed 9 (rogue and bard got a bit over-zealous on one while I was killing another, so we killed 9 instead of the required
. We ended up having to ninjaloot the chest and drop task/chain heal through it, and roll once the zone booted us.