Macatawa, no, if the grain is running perpendicular with the string you run the chance of splitting the shaft if the nock fails. Thus, in essence causing a dry fire and possibly do damage to yourself and bow. Having the grain horizontal to the string allows the energy of the string to push against the grain rather than with it. I hope I am explaining this correctly.
Imagine taking a knife blade and pushing it along the grain, the shaft will split easier. Now if you push the blade against the grain, it will be much harder as it won't give.