Actually Eels can get ich. Eels are pretty good at not getting it but its still possible and they can act as a host. I have a SFE in hypo right now with the rest of my fish due to a little ich outbreak from a new fish. Although the eel doesn't have noticible signs, I don't want to take any chances.
DUM DUM DUM, I always quarantine, but this time I was just in a rush.. They are all doing well in hypo though.