I don't imagine that it will do anything to corals, but they are ambush predators that will eat anything that will fit into it's very large mouth. Mostly fish but I'm sure it would eat other small critters as well. It's a lot of fun to watch them eat! If you have a predator tank setup, it should be fine. Some of them bury themselves in the sand to help with their camoflauge and ambushing, though, so you may end up with a bulldozer on your hands.
As a side note, the LFS where I work got a few unexpected freshwater stonefish (cousins of scorpionfish) in a shipment a few months ago. The brilliant manager, not knowing what they were, put them in a tank on the bottom row...where children put their hands all the time. I don't know how many people touched those buggers before we figured out what they were. 8O 8O Yikes! I can just see the lawsuits piling up...
Sara