....With flat dawn or other blanks you will get better interlocking fibers in one direction than the other. Worst for chipping will be true 45 degree grain structure to the face. You get extra short interlocking fibers along two edges or corners. These are more prone to chipping....
By interlocking fibers, do you mean between the early and late growth that form one growth ring?
I believe it is very unlikely not to saw across growth rings. A blank that has quarter sawn grain flow will have growth rings that continue into the blank. But, I believe importantly a rift grain orientation will also continue into the blank.
I think the problem happens when grain runs off the face of a blank or a finished stock. Chip out seems much easier on the very acute angles of the growth rings that usually look like like a plywood puddle on the face of flat sawn grain orientation. Of course, high figure could be the most prone to chip out, not because of the appearance but because of the random grain direction changes.
Luckily, I believe walnut can be very stable. I believe the bulk of stock shaping and majority of rough finishing is along the length of a stock. If tooling picks up a catch on 45* grain orientation, it might be easy enough to just change the working direction, but that blank may not have been sawn for gun stock use in mind and might be one that breaks easier than expected. It is completely acceptable, but along those lines, I prefer not to see those little grain triangles at the edge of action inletting or at the toe of a butt.
Jon, you've probably fiddled with more walnut than I have, it's just some thoughts.