NO, not at all. They wouldn't be good with any really tiny bottom dwelling fish though, say under 1.5" Other than that they don't cause any problems at all in my experience.
Jim
Sally light foots will not often venture out onto your sandbed. They prefer to live on the rock so they have a quick retreat into a crack or in between rocks when threatened. I don't think you have to worry about fish with them either, just about other sally light foots in the system, as they are aggressive towards each other.
Mine is in a tank with two mandrians and many corals, snails, grazers and so on and I have never seen him intentionally mess with anything. He does sometimes get startled and shoots across the tank....and they are quick !
they are fast. i have one for about 6months and the first month i thought i lost it to another animal. Eventually the sally appeared to my amazement. I watched it closely as it was picking debris from a rock with tiny polyps and it looks like it's eating them, but not so. The polyps quickly retracted until sally was done and gone. I tranfered it from a 55gal to a 50 and it jumped out onto the floor i put it back and was lucky to catch it again. They are extremely fast. nice addition to the tank.
I had a buddy who had lost 7 fish before he caught his sally in the act grabbing and killing a royal gramma.... All crabs are a risk in a reef with small fish and inverts.
I used to have one and it did stay on the rocks,,,, most of the time. Occasionaly it could be found on the sandbed and as quick as it would devour live brine floating by I'm betting that it would make short work of any worm, pod or small snail such as a nassarius.
Mine did get big, and did eat snails.
Be carefull.