My ex is a white boy in there that grew up in the hood of Atlanta, how would he be treated (by other inmates) since white population is so low?

If he is cool and understands the rule of respect, he will have no problem. If he knows the streets, he can survive prison. Gangs are another story. If he is white and not in a gang, that is a good think in the eyes of the blacks. But, honestly, there is a lot more tolerance in the world today between races as long as there are no gangs involved.