Hi rambunctious Rambo! Yes, Yoda still humps even though he was fixed, but we feel it's a normal healthy activity for him to do. He thoroughly enjoys it and he does it once every two days or so. He humps his stuffed kitty, however, if your Yorkie is humping your leg or a visitor's leg, then that's really something they need to stop!
That said, it is a good idea to get Rambo fixed if you are not planning to breed with him, as they will go crazy around females when they aren't fixed.