The Finalcut Pro 10.5.4 Capture does not work with the zfs-macOS-2.1.0rc3 release. It worked earlier, I can confirm, with the earlier Finalcut 10.5.3.
When capturing from camera, the movies do not get listed in the event. They are however, in the "Original Media" Folder inside the Library Package -> Event Subfolder.
I tried with mimic=hfs and apfs and off, no change in behaviour.
Look at this Feedback I wrote to Apple: https://feedbackassistant.apple.com/feedback/9494064
However its unlikely, Apple will do anything about it thus I write here as well, because Media management is one of the big use cases of openzfs.
https://support.apple.com/de-de/HT200243