I'm thinking that a vegan diet low in processed foods will mostly be bad for the lack of nutrients in it- the fat-soluble ones such as A, D, and E, the B vitamins, etc, as well as the lack of natural omega-3 oils (I don't think the plant-based ones work quite the same way).
Thinking about it, most of the "heart healthy" is based on the misconception that fat causes heart disease. In reality, it is injuries and inflammation of the blood vessels that then have to heal over. If the vegan is avoiding things that cause the damage and getting all their nutrients, I can't see why a vegan diet wouldn't be healthy.
That being said, veg* can be very difficult for a lot of people to do properly without becoming malnourished.