The snowflakes are a different genius than the" true" morays
Snowflakes naturally prey upon crabs and shrimp not fish. The the conical teeth or crushing shells not grabbing fish.
That is not to say they will not eat a fish if they can grab it. They are clumsy at chasing fish. They cannot see well and seem to hunt by smell . If lucky he may learn to leave "your" fish alone. I doubt he will mess with anything much bigger then his mouth.
They are strong burrowers. They will move anything that's in the way when constructing several burrows. So yes, he might move a frag or two. Just watch him as he settles in.
They mostly move around at night.