Some people have to remember that there are sooo many different types of mental illnesses out there, some more severe than others, some barely affecting the person. Majority of people don't even know they have a mental illness actually.
I would date a person with a mental illness, but to an extent, if its barely noticeable then why the f not?
I'm not sure, I've dated someone with a mental illness, that wasn't always prominent but in the end I felt defeated by it. If its under control and I knew the signs when they were feeling down or whatever it may be because of it I would consider.