Jamie, like you, I like my bows leaning toward the short side, narrow, heavier in draw weight, radiused bellied, almost always osage, and yep bamboo and osage are a special match.
I have used hickory on lesser woods with success, sometimes very thin hickory, and burnished it... which may have helped???
My problem with using wood boards for backings is possible degredation, but also, like Mike alluded to, if I didn't see it standing and split it myself to know how the grain runs, how would I know?
Understanding that grain runout and ring runout are two completely different things, how do we know that a quarter or rift sawn piece hasn't had its grain violated enough to be a problem? I suppose we could try to buy a piece long enough or wide enough that we can cut a piece off and do a test split.