if my memory serves me well, there are some different breed of them. your pair seem to come from the isengard - as treebeard suspected, cross-breed between humans and orks from misty mountains, who don't like sunlight but still can fight in the light of day. there are also big, ugly uruk-hai from mordor, more animal like, and also one smaller breed who used to inhabit minas ithil and cirith unghol - guys who made frodo and sam some trouble up in the mountains (what was the name - snaga?). so after all, you are maybe right about them :-)