I have both a reef and an aggressive and a reef w/ eel tanks. Tessys and greens will eat everything -- snails, shrimp etc.... SFE, zebras, striped etc.... they are normally crustacean eaters. However, every eel is different. I had a SFE that would eat shrimp and everything else all day long, then I have had one that only would eat via feeding stick or if I put squid in front of his den.
Worst mistake was not finding this out before and having to break down my reef tank to get him out -- the SFE that ate everything. Also, as mentioned above, they are messy eaters. You will have to be very vigiliant about water conditions.
Remember, the cute SFE that is a foot long in your tank will grow. But, remember that they are carnivores, your crabs, shrimp and snails might be in danger unless you keep up a strict feeding schedule for the eels.
Good Luck