The vast majority of biologists are against using any captive bred animals that have a questionable genetic history. That means that its very unlikely that the animals we have in the hobby will ever be considered for use in conservation. This is mainly due to the risk of hybridization and excessive inbreeding. If you create hybrids it won't really matter in a conservation sense. That's not to say that hybrids don't happen in nature; they're certainly more common than most people think, but we still have distinct species even if a good portion of their genome didn't originate in their specific species. I personally don't like them because I'm into natural looking fish (with a few exceptions). The only aspect I'm against is the possibility of the extinction of parent species in the hobby, which is pretty common in some hobbies that I'm a part of (ie Brachypelma spp.,).I don't keep hybrids in my tanks.
My reasons are that with the destruction of species by our activities, we may end up with a lot of fish that only exist in aquariums. We already have fish whose habitats are gone. If we keep crossing species, we can drive creatures like that to extinction, via hybridization. You can combine two species and make one hybrid, and in the process, lose the two species.
However, if you don't breed fish, keep all the hybrids you want. Fish kept as ornaments aren't going to affect anything.