In Kingdom hearts 2 you fight side by side with multiple FF character. They weren't REALLY in your party but you did fight together.
Auron was a party member in KH2. Zack fights with you a bit in BBS if you count it.
Oh right, forgot about that.
Yeah, in terms of party there was Auron in II and Cloud in RE:Coded. I remember the Radiant Garden scene too where most showed up as AI. Maybe it is a possibility.