We recommend against that. See Why NOT to run Opus as Administrator under UAC
Correct.
But the options for copying permissions/ownership only apply to Windows file permissions/ownership. I am not sure how Samba or ZFS will treat Windows API calls to query and set permissions/ownership when Windows and Linux use a different model for those concepts.
Folder dates are also fragile, since anything that changes the directory listing can bump them. (Although that also depends on the filesystem and OS involved. It's a Windows convention but other OS may be different.)
And servers, especially ones running other operating systems, are free to ignore or reinterpret requests to do with metadata.
Have you tried the same sync between two local drives? That should show what Opus is doing. If that works but you get different results with a Samba network drive running ZFS, it's likely the problem is at the other end or a limitation of which Windows API actions Samba can bridge to the Linux world.