No eels are totally reef safe. They will hide behind rocks, dig holes when they swim, are very strong and will re-decorate your aquascaping, not to mention that they can break brittle corals. And to top it off, they will eat ANY fish, crab, shrimp clam that it can fit into its mouth. They are very messy eaters and give off a lot of waste, so you have to be carfull of amonia\nitrite\nitrate spikes, so make sure you have a real good skimmr.
That said, I keep an eel in my reef tank. It can be done, its just a lot of work, but well worth it.
Bill The Cat For President!