There are a few low-level gnolls on the trail leading to the vale and then once you enter the vale itself, you are greeted by large packs of higher level gnolls. The gnoll packs are on a five minute real-time respawn timer. You can choose to ignore them but they'll likely run into you and complicate your fights if you don't.
The druid ring at the middle of the vale is surrounded by Sabertooth oracles. Clear all of them to spawn the named bosses; all four of which are worth a bit of AA.