In Redemption, that guy who went to the president's son for help said he knew Voight was some big shot, but didn't know his name. So he can't be the VP.
Lennox worked on the staff for Wayne Palmer and Daniels. The exchange in Redemption made it look like President Taylor beat Daniels in the election, so that would rule out Lennox, well, that and the fact that Lennox was also there for the exchange of power. That also makes him from a different party, but then again, that didn't stop Mike Novick from working on the staff for both David Palmer and Logan, who were from different parties (Logan replaced Keeler, who was running against Palmer in season 3).
Heller has to be out of the picture. They've effectively cut Jack off completely from his entire past. Bringing him back would re-open the Audrey door, which I can't see them going anywhere near. He should be in the same party as President Taylor though, so I guess anything's possible.
Maybe I'm overanalyzing the whole political party thing, but the whole Mike Novick situation always bugged me. Being the top advisor for two presidents from different parties?