Do people who were born blind, see dreams ?

No, they wouldn't. Visual stimulus is necessary for the wiring of the brain centers that process and interpret vision. The way the brain works is to develop, early in life, a huge number of neural synapses (connection points between neurons that are used in cell-to-cell signalling). As you grow and learn, these synapses are pared away to make the brain function efficiently, and that's the central basis of long-term learning. However, if the brain or any part of it fails to get infromation from hard-wired inputs, then that part of the brain will atrophy (at best, fringe areas of a cortical region might be adopted by adjacent cortical regions for different processes). But the take-away message here is that the brain needs visual stimulus in order to devolp the cortical regions that process vision. In the use-it-or-lose-it sense, the brain will not waste energy building and maintaining processes that aren't used. The optical cortex would never know how to function as an optical cortex in a person born blind.