Goldfish are about the best option for the BH because they do very well in coldish water, and they eat algae. Over the years I have seen Carp, Piranha, trout, and a few other varieties in BH. GF, and Carp seem to do well, most others don't.
GF are NOT surface feeders. The issue we had in releasing the GF was that the outflow can and does carry fish away. In addition the flu was raised at some point and the BH lost a lot of fish, not just GF.
I think dumping a bunch of GF in the BH on a regular basis is a great idea. Unfortunately most will NOT survive, but some will. That is just the nature of life. If we want to see an increase in fish population, then stocking the hole is a very good idea. Unfortunately for those of us living 5+ hours away from BH, hauling GF is a bit of a dicey task.
KOI would make an awesome addition, but they are bit pricey. Someone mentioned pulling some KOI out of their pond and dumping them in the BH, but I don't think that ever happened.