I think it very much depends upon how you personally experience depression. For me, I know that there would be no chance that I could be creative. I am a writer, and depression just brings a cloud over me meaning that I'm not able to write anything. However, I have a friend who has depression who uses painting as a way to help himself, and I know that he would say that his depression has caused him to be more creative than he would have been in the past. So everyone is different, it would seem. It is also interesting to look at bi-polar depression, as there are many records of people being incredibly creative whilst at a "high" point. This is interesting, though I know that you meant uni-polar depression from your post.