The AZA would (or should, anyways) really only actively discourage institutions from acquiring a species if it is in direct competition with one of their programs. Bush dogs are not a species that will really be competing for space with other species, seeing as the only canid species from the Americas the AZA manages are the three species with wolf in their name, each of which is much larger and has much greater spatial requirements. I highly doubt the zoos that would theoretically get bush dogs are going to instead use that space for a different canid if the AZA doesn't want bush dogs, so not really a concern in this case. Granted, there are cases where, yes, it makes sense for the AZA to actively discourage institutions from housing a species. Striped hyenas are in direct competition for space with the SSP-managed spotted hyena, and there isn't room to manage both species. Same thing with sun bears taking space away from sloth bears. Bush dogs really don't fall into that same category.