I believe they will dream in however they perceive the world. As a seeing person, I cannot imagine what form that would be but I imagine it would include much more of their other senses than I have when I dream. I have had dreams where I lose my sight where my peripheral vision starts to go black and then grows inward until all I have is a pinpoint of light until even that is gone. I usually wake shortly after that but I remember my focus changing from sight to sound and touch and my senses extending outward to try and feel the space around me to try and sense other objects. It is a very interesting experience but scary.
