As the other answers thus far state, they do not see in their dreams, due to having never seen before. That being said, it has become technologically possible to grant eyesight to those who were born blind. The FDA approved a bionic eye on February 14th, 2013. With it, they might be able to see enough to start dreaming optically as well, but I am not aware that any such studies have yet been made.
Googled 'Bionic eye'
Googled 'Blind people dream do they see' (Autocompleted by Google after 'Blind people dr')
Looked through the search results of numerous similar questions, and formulated a concise answer.