Choked to death? Further info, like what it was eating or if it was, would help.
A 180 gallon will hold those guys for a little while, but the aro and gar will definitely be needing a MUCH larger tank eventually. So, if you're prepared for that, and the aro and the gar will be moved when large, then the fire eel could be a consideration.
However, depending on everyone's sizes, I would have a concerns that the eel might look like lunch. A pleco in with the eel can have its problems. I have had certain plecos that will try to munch on my eel. I have a pleco in with my three eels currently and they're fine, so with certain plecos it can be done. The arrow and the gar are the big concern to me. A large arrow or gar (I believe up to 3 feet for both) would easily see a fire eel as a snack unless it was already gigantic. Evens still, I still would be worried they might snap at and injure the eel.
Seeing that you're asking, I think you know it is risky.