I'd be surprised if Disney provides bus transportation from resorts to the Braves spring training venue. My experience is that the fans at the games don't come mostly from Disney hotels. They sell seasons tickets like any other spring training venue and single game tickets are pre-sold through Ticketmaster. I usually see local people, lot's of retirees from Georgia, other Braves fans and a good smattering of folks who follow the "away" team who aren't necessarily in the area for anything other the games.
So, if I'm right about Disney providing tranportation for the benefit of another corporation (the Braves), then you'd have to find your way by taxi. I'd call your hotel to find out if you should expect Disney transportation.
The ballpark is a really nice facility. Enjoy the game.
Dick Taylor