I'm very familiar with this as I spent 10 years in prison. The term "Uncle Tom" is not used by black men in prison. They say "house n-word" (except not n-word of course). It's about the most offensive term possible.

It basically means a "house slave" that was well-treated and is therefore sympathetic to or on the side of the white man. The anytonym is "field n-word", a slave that worked in the fields, which I probably heard more often as people sometimes identify as that term. E.g., if a guy is talking to his buddy who has a nice ("cadillac") job situation, he might say "I'm just a field n-word."