The definition of a nuisance can be broken down to basically mean "bothersome" or "offensive". Homeless people don't usually bother anyone. The occasional begger who asks for change, but really that's not much of a bother unless they are persistent. But this is not the majority of homeless people. Why anyone would be offended by the fact this man has no place to live is beyond me. So no they aren't really a nuisance, only the rare persistent begger.