It's probably different for elite baseball players like this, but I know the guy who drafted Cedric Benson for the Dodgers. The Dodgers paid him a bunch of money, let him play football (where UT did not have to give him a scholarship because the Dodgers were paying his tuition) and then Benson didn't come back to baseball. The Dodgers felt foolish. According to my friend, baseball teams are less likely to go down that road now. This came up when the Royals drafted Doherty.
But, like I said, maybe the A's drafted him after Murray told them he was playing football this fall and it was non-negotiable. He's elite. He has more leverage.