Although i cannot comments on the use of macos 9.1 with ipod, here's what works for me..
I have an ibookse (g3 466mhz) with macos 9.2.2 using itunes 2. Works perfectly. I used to have macos 9.1 and itunes 1, but didn't even bother trying it out with the ipod since it wasn't supported and troubleshooting would have taken longer than upgrading.
Are you using itunes version 1 or 2? what hardware are you using (shouldn't "really" matter in an ideal world).