I may not post on here much, but that is one combo I have done for many years, and will say 100% works GREAT!!, I had my last Fire eel at 28-30" (3.5-4" girth) and never once had an issue with him and my rays (male 10-12", female 14"+, (disc size)). they always got along great, i have since lost my eel due to other reasons (hard to keep long term(bacteria infections)) but that is deff one of my fav combo's i want another eel, but i am gonna wait till i can get a much bigger tank.
Sean.