After further trial, error, and profanity, I narrowed the main problem down to the image map node, when I discovered that procedural materials still rendered properly on the fur.

It's the texture-filtering option.  P8's texture filtering goes absolutely insane on image maps plugged into dynamic hair.  The results may vary with different maps, but the only solution I can think of is to disable texture filtering completely on those.

Here's the same #@$&% scene file in P8 again, this time with filtering disabled on the hair maps.