That's a difficult question to answer. I don't know anyone who has kept a snowflake (moray) eel with clownfish in a tank? The eel might find the Tomato clowns delicious if he finds them away from the anemone at night, but if the clowns are hunkered down sleeping in the bta they might be safe from predation?
I have a pair of Tomato clowns. I happened to turn on the lights early today and they were hunkered down nicely in their bta. They decided to bite me while I was working in the tank, they seem to be protecting eggs again? Because these fish are so territorial I think I might add the eel first and let him find a place to hide and then add the nem and clowns at the other end of the tank to keep them separated as much as possible at first.
If your clowns get eaten hit me up, mine have been acting up lately and it's getting old.