eels in a cichlid tank?

It mainly depends on the cichlids in question. If they're large enough to eat the eel/s, obviously not a good combo. Small or mid-size cichlids would be fine wth a fire eel or tiretrack eel, provided there's sufficient cover for all concerned. If they're African Rift Lake cichlids, and the tank is large enough, elipsifer or plagiostoma spiney eels aren't usually bad choices unless you mind them eating the eggs of substrate-spawning cichlids. Cichlids tend to ignore eels (other than as prey if small enough to swallow), probably because their body shape/color/patterns are so different they aren't seen as direct competition.
As for eels other than the spiney eels, not a good idea for various reasons.
 
I have a 20" Tiretrack in my 150 with an oscar, about 11 peacocks, 6 spotted silver dollars, 4 bristlenose plecos, a common pleco, 2 Synodontis eupterus, 2 bichirs, and a compressiceps. If anything the eel is the dominant one.
 
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