He'd sign it if it was the only chance he had of getting a bigger contract. Baseball players also tend to have sizable egos when it comes to their talent, there's a decent chance he thinks he'll prove his worth and get those PAs. And with the context in which the "jesus" was originally used, it was an invocation of protection, much different from using it as a curse. I suspect most people don't consider begging god for help to count as taking the lord's name in vain, although situations like this tend to trivialize the use