I have two eels in my tank, a banded snake eel and a snowflake moray eel. I also have 7 blue-green chromis, a yellow-tail damsel, and some other small fish. I used to have a bi-color blenny, but he dissapeared. I've also had a chromis dissapear and another show signs of getting attacked by something. It was likely the eels, but it could have also been my large maroon clown. I don't think I've seen any loss of snails due to the eels, but I could be horribly mistaken on that front.
The bottom line is that eels are aggressive predators and if you don't feed them well, they WILL go looking for food. Just keep them fat and happy, and everything else will do just as well.
