not an expert on fire eels however I have been doing quite a bit of investigation on them and meeting with a 3 foot one Snuffles about 2x a week....
They like a planted tank the heavier the better... Memphis is loving the tank now that it is just him and the catfish both shy sorta he loves to sit on his tail and watch me
I have had Oscars and they love to tear the plants up just for fun

nothing more they do not eat them, just rip them up
The eel likes the sandy bottom and the oscar will just toss it around again for no reason the Oscars seem to love to move anything you put in the tank

as if to say it is my house and I want this over here......
so you will be forced to have your hands in the tank quite often and dep. on the eel he may have an issue with this
then it comes down to feeding Oscars seem to eat very quick grab it all and run while my eel likes to sit down with a small pile of worms and eat one at a time

I do not see an Oscar waiting his turn or even sharing
my vote would have to be that these two fish are not ideal house mates. The rope fish is more outward going that might be a better fit.

If you really want one because they are so cool get yet another tank

that is what I have done
1 tank for puffers
1 tank for fire eel
1 tank for cichlids
1 tank for shrimp
1 tank for corals and Nemo
1 tank for Guppies
cleaning is an all day thing here
