[mormegil]

My feelings is that they felt personally and believed Sauron viewed them as superior to orcs in every way, with the exception of making good cannon fodder which orcs excelled at. Contrarily I think orcs viewed the humans as weak and not as useful as themselves.

When they were bent on the domination and destruction, I feel that such an inconvenience as fighting along side orcs was hardly a major concern. Think of it this way: The orcs viewed themselves as courageous and indispensable at being sent as the front line of attack for battles ergo their position was more valuable to Sauron and they served him better in their minds. Men were a bit more intelligent and realized that they, the orcs, were being used as fodder to soften up the opposition and would rather be used for the more strategic and final blow offensive (think Oliphants). Either way, Sauron, made both people feel appreciated and needed. I view this as the relationship one not liking the other but liking their own position more than the others.