This is an old one, but I'll chime in just the same, I voted yes to most carnivores. The better word would be predators, after all the Zebra pleco is a carnivore as are many fish that do not eat other fish regularly.
I do not, have never, and will not use goldfish, I raise my own guppies, snails, and am working on shrimp. Goldfish provide little to nothing but a big mess, all of my fish will eat prepared foods so the live stuff is a treat for them. I personally think it is wrong to haouse an animal who likes to hunt an then never allow that animal the opportunity to hunt. Everyone has their opinion on this, and I am only stating mine. Certain fish are designed to hunt and should get to. With the Sa cichlids I keep, feeding a high nutrition diet is easy and the live stuff is used for the treat and natural instincts of my fish not for the purpose of sustaining them nutritionally. Unlike many folks, when I first started keeping Oscars and didn't know any different it never really occured to me to feed them anything but fish food. It works, but my Oscars color up better, and have more natural pesonalities when they get to hunt whether it's snails or gupies or shrimp it doesn't seem to matter, most bugs work well too and also earthworms. All at levels that don't create excessive waste in my tanks.
On the thought of Goldfish themselves as opposed to other feeders, every single Oscar I have ever seen with hith has been fed goldies This doesn't make it a fact that goldies cause it, but it's enough of an issue that I won't allow them in my tanks. I have never had a case of hith develope on a fish in my tanks, and am only familiar with HIth though adopted fish that were in poor shape when I got them.
Dave