Pete, If I find a perfect looking board I will use it for a selfbow. I have made a few with very slight run-offs, but only in the grip or tips sections. I prefer flat sawn, but have used boards cut every way with bamboo just to see if they work.. On a board with highly visible rings you could follow one, but I have never bothered..
Years ago I made a longbow with several good run-offs to abuse on the tiller set-up just to see what it would take. Frankly it took a lot more than I thought it would, and if I hadn't blown when I tried to bend it into a circle on the last pull, I would have backed it with bamboo..
So I know you can have some "grain deviation" and get away with it..I just can't say it's "ok" for ethical reasons, and I don't want anyone to catch a limb in the noggin..
Rich