Hugo was not attempting to write a historically accurate portrayal of the time. Thus 1482 is merely a setting for his novel, its the equivalent of 'a long time ago'. Any portrayal of gypsies as such will be almost entirely reflective of Hugos opinions of how he wants them to be used within the context of the story.

However he uses Gypsies as they are a readily identifiable ethnic Trope that his audience in 1831 would have understood as a potentially viable persecuted minority. Its unlikely that the 1830s audience would have been been particularly enamoured with them, as otherwise their figurative useage within the context of the novel wouldn't have made sense. For example if he' swapped out Gypsies for Swedish people then his audience would have been puzzled and asked 'why are there so many Swedes in Paris and why would they be persecuted?', it wouldnt make sense. However no one would question the Gypsies in that role.

Romani people, then as today, have operated a slight step outside of the local community and thus have often been burdened with negative attitudes. Whether these opinions are valid is a difficult area to be certain about. Its true though that many people still think so.