They have done so in Japan. https://www.researchgate.net/public...r_hassi_Heterocongrinae_observed_in_captivity
That's the paper I was going to link to as well. About 300 Garden Eels were kept in the tank at Sumida and spawning was observed. The eggs were fertilised but no larvae survived after hatching. So the answer is that they have produced viable eggs in captivity, but that's as far as it has gone.