That’s an interesting one. I guess it depends on when they person became blind. If they were blinded during life, then their visual pathways in the brain would still be intact and they would probably still ‘see’ in their dreams. If they had been born blind, however, the vision areas of their brain would not be used for vision (obviously, because they’re blind!) – instead, those brain areas might be used in other processes, such as to enhance their hearing. As a result, they wouldn’t see things in their dreams as people with normal vision would do, because their brains simply don’t have that sort of circuitry.