From what I've read, no, the north facing panels really won't contribute to the heat generation. I tend to be an advocate of "get more early" for solar panels. Mainly because I've learned the hard way. I am in the process of adding a 2nd bank, not so much for absolute temp increase, but for quicker heat recovery after bad weather. But, north is just not good with solar panels, the sun is not on them long enough.

However, the angle of the roof definitely makes a difference. If you have a flatter roof, maybe it will work. I don't think it will hurt. Push come to shove, I think I would do it for 200 bucks.

One thing you might consider is going to powermat.com and looking at their powerstrip line. These can be custom cut and constructed so they can often provide more coverage (they be setup to follow roof angles, etc.). You might be able to use more of your roof with these.