I am no doctor, but NBA teams and players have access to some of the best available worldwide.
My question is, if he stood no chance to make it back, then why would he go through the effort to attempt to and why would multiple NBA teams offer him a contract?
For Oden: he has 1.1 million reasons to go through the effort!!
For the NBA teams: You can't teach height!!
Plus, as has been pointed out, it's low risk/high reward!! If he doesn't work out, the Heat are only out $1.1 million. If he does work out, they'd be almost a lock to win the title!!