Yeah, he played Ansem in KH2 and what few voiced scenes in 358/2 Days. Corey Burton did his voice in everything else, including redubbing his scenes in Days for 1.5.
Man, my heart broke when I heard he died though. As far as KH goes it won't effect things as much as Leonard Nimoy to Master Xehanort will though. Corey Burton at least for Ansem is a good soundalike.
the cast is dropping off quickly, not to diminish an actual death of a talented actor, but kingdom hearts 3 is gonna be a very different sounding game.