I just farmed 16 of these for 2 alts doing the shawl quest. Took 55 velium hound kills, so almost exactly a 30% drop rate, not too bad.
The first night I was there, didn't come across many hounds after the first clear. The next night, I had seen the comment someone left about also clearing the mastadons and brontotheriums. Doing that improved the spawn quite a bit.
Also, I wouldn't want to even consider this camp without a tracker.
Tat