They are generally safe with corals. Smaller fish and crustacean are the main things they'll become a threat to.
Other than bumping in to them, I don't think I've ever heard of one bothering coral. Clams, occasionally.
They can become fairly pugnacious as adults as well - hopefully you've got a big tank for him! Much like tangs and triggers in this regard - fairly peaceful as juveniles, but can become quite aggressive as adults if the tank is not very large indeed.
