I'm running Crucible 2.8.0 without Fisheye, over a Perforce repository, and cannot get pre-commit patches to anchor successfully to the repository.
I could not find an open issue regarding this in the support portal.
Do I need to install a full-fledged Fisheye instance to get anchoring to work?
Yes, anchoring essentially means connecting the files in the patch to their correspnding files in a FishEye repository.
Anchoring allows Crucible to present more context than is available in a patch upload. It uses FishEye as the source of this additional context.
You can still preform a review on the patch without anchoring. You just won't have access to the extra context.