Corals would be totally fine with any eel - with the caveat that they're gonna poop lots so your tank needs to be able to handle the extra load. Other than that though, corals aren't at risk. What is at risk is any critter that can fit inside their mouth.
The golden dwarf eel is small though. They are the same size, more or less, as a pencil, and as such, there's not much that can fit inside their mouths. They max out at 12" long. Mine is around 7".
But eels are notorious for getting out as they are curious about anything they can stick their heads into. I had a golden dwarf in a 20g tank last year, I had that thing locked down with covers and he still managed to get out (and perished
)
This guy I have in a 30" tall tank and the rockwork only extends up around 14" or so, so there is at least 15" of open water. So far, he is not interested in swimming out in the open, they know they are small and thus they are pretty shy. The only cover I have is eggcrate and I'm fairly certain it would not stop him if he wanted out. However I think the height of the water column in this case helps a bit.
The next smallest eel, IIRC, is the snowflake. I hear of many reefs keeping these. Although they are usually available in the 8" size, they do top out around 24" so I think they would be a little more adept at crawling out. And I would think they are big enough to take down things like cleaner shrimp and whatnot, although I'm not positive on that one.
A canopy should help, I would think. I don't think they jump per se as they slither out. It would be fairly difficult to slither UP a canopy wall though, so I think a canopy with the holes covered up (foam or whatever) is a good idea.
Usually the bigger eels seem to require FOWLR setups and I imagine it's really the poop issue and the "will eat anything that fits" issue that really drives that.
That about sums up my total knowledge on the topic though. Others out there may have "more better advices."
