It depends. Some eels are tolerant of other eels and some aren't. There are quite a few combos of tankmates you can have with eels. I've had eels in every tank...African cichlids, datnoids, vampire tetras, rays, etc. I've had a tiretrack get along with a fire eel and I had a combo of the same two species (different fish) that did not get along. Right now, I have an 18in tiretrack in with a 10in fire eel and though they are in the same tank, the tiretrack harasses the fire eel every chance it gets. Fortunately, its a 320 gallon with tons of hiding spots so its chances are minimal.
Hope this helps.