From what I have heard, you shouldn't have any problems with the snowflake and corals. I think the snowflake would only give you problems with smaller fish. I have a niger trigger in my reef, and from my experience, the niger is just fine in a reef. He is more aggressive towards fish than he is toward corals or inverts. I've never seen my niger pick at any of my inverts (hermits, CBS, starfish, emerald crab, etc.) or any of my corals. He did show some aggression towards a very small fire goby once. The goby was significantly smaller than the niger, and it didn't last long in the tank. That is the only time he has ever gotten aggressive.
That's just my experience, so take it for what it's worth.