Heartless are actually hearts, and since Ansem SoD took home in Riku's body, his heart was there for the last part of KH1 and possibly all the way 'till near the end of KH2.
That doesn't mean he wasn't able to. Eraqus, MX and Terra could all wield. Are you telling me Ansem SoD wouldn't have the possibility of being able to with a heart that is pretty much three wielder's hearts?
Uhhh, how are those situations at all the same? The keyblade came to Sora because he touched Riku's heart and swiped the Keyblade away from him.