It's not connected. Well, part of me hopes it's not. Not up for Marvel characters in the Kingdom Hearts world or vice-versa. However, the possibility of these two tweets being unrelated is greater than the opposite. Simultaneous tweeting isn't some dead giveaway.
While I wouldn't mind Marvel in KH, I actually don't think this is what they tease. But I do believe these tweets are more than a coincidence. I'm betting on a Marvel game developed by one of Square's western studios.