Me, quite important, though 'hygiene' and 'appearance' for the most part are somewhat interrelated.
Unshaven/bit of stubble is ok, if it helps compliment some look; unwashed hair or bad hair day is not ok.
If I know I am going to be seeing an SP, or at least want to be prepared for, I'll make sure that I've groomed for (manacape, etc); if I haven't, I often won't take the chance on a new provider.
This is all about minimizing chances of a bad session or being on the wrong side of YMMV; if there's anything simple I can do to reduce that risk, I do.
That said, I don't feel that I/you should need to look like a GQ cover model to see an SP.