FTT: My first choice would be the vulture cat. It seems that they have a range in max size from 14-18" or so. It seems that a lot of the bio information points to them being a bit aggressive but a lot of the first-hand info I found says that they are not aggressive towards their tankmates, unless tempted by a very sickly or injured tankmate, or become desperate out of extreme starvation. Therefore, it seems that one would be fine with my fire eels. I do worry about the size but if the fish I get ends up maxing out around the smaller end I think it would be fine. Of course, if it ends up being one of the larger individuals nearing 20" or so, I would rehome it, but certainly wouldn't hope to end up in that situation.
TBTB: IMHO you can forget about the 14". I've never seen a mature vulture this small, not that I am "I've seen it all" but I don't think this can be relied on at all, again IMHO, is all. I think you can bet your vulture will attain 18"-24" TL = total length. Among my six 2-year-olds, the two biggest are 20"+, two medium are ~18", two smallest are ~16".
So I'd think you either have to upgrade your tank to 500 gal like 8x2x2, which will set you back ~$2000-$2500 delivered (if acrylic), and then you can have several vultures, or forsake the vulture idea. On the other hand, in 220 gal you may have a few years, for sure 1.5-2 years before you will see that 220 gal is too small for an average-growing vulture.
Furthermore, vulture maxillary barbels are very long and an 18" vulture will cover 2' in the barbel span. When both barbels will be able to simultaneously touch front and back glass, it will feel trapped and will get nervous, skittish, etc. Not a healthy way to keep a fish.
FTT: Next up is the bolt catfish. This seems to be a smaller, slimmer version of the vulture cat. The coloration is not quite as appealing, IMO, but very close. My concerns about the bolt cat are it's darting movements and aggression. I would be providing plenty of hiding places for both the catfish and the eels, so as long as that will keep the aggression from happening, I would think it shouldn't be a problem. The size of this guy seems to max out at about 12", so it should be ok size wise, but with its darting movements I do worry about a 220 not being large enough to keep it from banging into the walls of the tank.
TBTB: I have been wrong before once or twice (sarcasm) but I'd not worry about the bolt's quick movements. They are not from skittishness but its nature, kind of the same as pictus, blochii, etc. It will not hit walls. Mine have not done it anyway. The aggression again I have not seen but I've not kept them with fire eels. They seem to not care about who their tank mates are.
Bolts are kept very rarely. In fact, no one comes to mind at all, now that I am straining my memory to even recall a tangible bolt account / thread. I do hope someone else will chime in but I'd not count on it. For every bolt it'd seem about 100+ vultures are kept so I'd expect more people to be able to help you out.
FTT: ... One last thing, my eels are currently about 10-12" long, but they've been growing quite fast over the past few months in the 29, and I expect that they will probably speed up now that they are finally in the 220.
TBTB: It can vary but in general fire eels don't grow fast. I've got 5 black spot, 2 tire track, and two fire eels Summer - Fall 2015, all at about 10"-12". Lost one black (at 21") and one fire (at 10"). Today the 4 black spotted ones and 2 tire tracks are ~2'. The remaining fire eel is about 14"-15". In fact my experience with the fire eels has been pretty miserable - I've tried them 3 times (all around 12") before this time and each time I couldn't get them to eat anything but live ghost shrimp. This last one is the only survivor from my cruel experiments with the fire eels. Spotted and tire track eels I've never had a problem with, they eat a lot of foods. Fires are so exceedingly picky! The survivor would only eat thawed bloodworms for a long time before eventually agreeing to take cut fish. The one that perished along its side, wouldn't have any prepped foods.
Perhaps my fire eel thumb is not there altogether...
Anyhow, sorry, long story short, IDK how vulture or bolt would be with a 10-12" fire eel. From what I have seen, I'd predict the eels would be safe but I'd not be blown away if I was wrong.