I think what I remembered was a cross between Gillmonkeys and Kech. I ended up using regular goblin stats, and just adding a climb/travel through trees speed of 30'. I described them as goblins with prehensile tails, and gave them "primitive" weapons. The PCs only ran into 4 of them (at 6th level) so it was a VERY quick and simple fight, but fun because the theif had strayed off by herself behind a tree, and got critted. There was much discussion of what exposed piece of anatomy she got shot in... and why she was having trouble riding, thereafter.
But later the PCs will travel back through the same region, and I think then they're going to run into the whole tribe. Any special abilities you think the "boss goblin-monkeys" might have?