It depends on the cause of their depression. There's many causes and levels of depression.
If they were depressed due to a relationship break- up I wouldn't, because I would never give my heart to a guy who was still picking up the pieces of his own. People need to heal before they can give a potential relationship a chance.
If he was deeply depressed and suicidal I wouldn't either , but I would reach out a hand of friendship to him. His emotional & mental state should be priority and I'd encourage him to seek professional help.
I have suffered from depression due to circumstances I was facing at the time, so I know how difficult it was for family/ friends to be around me. So it all depends on his level of depression and reasons why he is depressed.
Depressed people are dateable , but dating may not progress and develop into a relationship if the person doesn't seek help... even self- help. If a depressed person wants a happy relationship they need to put their mental state above any potential relationship.
Yes, I'd date them. I feel like I could actually relate to them in a way. I've never been diagnosed cause never went to a doctor or anything, but I'm pretty sure I've had terrible depression. I know how much a depressed person needs someone who truly cares about them, so it wouldn't stop me from dating them.