I have kept a snowflake, a zebra, a Hawaiin dragon, and a whitemouth. In my experience, the only type of fish that should NOT be kept with eels are wrasses and fish with a similar tubular body shape. For example, I am pretty sure that is was the snowflake that ate my 6" corris wrasse, and I am pretty sure that it was the whitemouth that ate my 5" salfin dottyback. I have also lost a few damsels to eels over the years (although I have an electric blue damsel that has been co-exisitng with the latter 3 of the above listed eels for almost a year now).
My theory is that most eels, even if well fed, will prey upon any fish that tends to sleep in, on or next to the sandbed.