Brittle stars and serpent sea stars are great for all reefs, including sps. I removed all the sea urchins from my systems because they will remove coralline algae (the purple stuff) from your system.....Healthy coralline algae in the system means your aquarium will be suitable for stony corals. You may be able to trade your urchins for credit at your LFS as well.
Brittle stars will not eat your fish, either.They are great scavengers and detritus feeders, which is very important to have for a reef environment....