I think he just did make it up. "Monkey up" is not a metaphor I've ever heard afore.
But then again I never heard of "Macaca" until George Allen or whatever his name was.
I have not only heard it commonly used, but also variations that coincide like "monkeying around" (goofing off and acting stupid). It is also kind of a short rephrasing (that is used to express the same condition) of another common phrase "throwing a monkey wrench in the works", as in screwing up a piece of machinery by throwing a large monkey wrench (pipe wrench) in it (or haphazardly screwing things up) .
From my point of view, you would have to want to be offended to take it the wrong way, and any racial connotation would be a product of people consumed by their desire to view racism in everything (and that's their stupid problem).