I played Joint Ops, you could get on pretty much anything, rock outcroppings, hut roofs, climb certain trees, you can get on top of btr's, tanks, etc., and even more so in the expansion pack Escalation.
Th33f played Soldner, and if I remember correctly, that game also had these features.
Making an animation for climbing should not be to hard. Is there a crawl animation, if so, turn it vertical, and you are climbing. You can't shoot while running, makes sense that you can't shoot while climbing a ladder, but once you have stopped moving, fire at will.