I beleive they will get along with an oscar, as long as the oscar isn't overly agressive. I would warn you however to not get this fish unless you're prepared to possibly have to feed it live food.
I have a peacock eel, which is in the same family as the fire eel. He won't eat anything but live food. I"ve tried every type of frozen food. The only one he'll even try is the frozen blood worms. He'll suck them up and then spit them back out again. Its not that much of a pain to feed live food, but it is a pain if you have to drive a half hour to get it like i do. I only feed him 3 times a week though, and he seems to be doing fine. Some people say they are able to switch them over to frozen food after feeding live food for a long time. I haven't had any luck yet.