You can get to the camp from the side of the Mountain Pass, there is a ravine here, if you jump over then it can lead you to the upper outer levels of the temple, not far from the bugbears and the wall.
You can also featherfall+jump your way into the camp from the cliff where you find Arka's corpse.
Can't think of any other ways for now. I heard something about the drow being able to enter the camp at will? Haven't played as one yet.
