I think you could and probably should make a case that the dog is inappropriate for apartment living as it could encounter other animals and children, as well as adults who may be anxious about the possibility of attacks. If you refuse permission on those grounds, the owners may challenge this at a tribunal, if they are so keen., but I can’t see how they would win.
One thing in your favour, anyone who takes a potentially dangerous dog into an apartment block isn’t likely to be super-bright themselves. As someone once said of American Pitbulls – they are dangerous, stupid, aggressive and ugly – and that’s just the owners.