I have been depressed before, but I don't believe I have any ongoing, persistent issue with it, though I wouldn't check it off my list. My most prominent issues are social anxiety disorder, which seems to have an impact in exercise due to almost constant anxiety, up and down elations of mood, and some self-image & self-confidence issues.
There are bodybuilders who have said they suffer from depression with amazing results, so this kind of boggles the typical, straightforward "yes" answer, because some have succeeded well in exercise while being depressed.
So to what degree does depression, anxiety/stress, etc. get in the way of results?