Unless it can't because you happen to have mounted your user cache directory from a different volume in an attempt to debloat your hourly backups.
Ironically, if my backup scheme were using hard links, then I could simply exclude the cache directory from backup, so I’d have no reason to do that mountpoint spiel, and uv’s hard links would work normally.
You’re correct, ZFS snapshots don’t produce copies, at least not at the time they’re being created. They work a little like copy-on-write.