I have two similarly configured Mac Pros both each with a zfs-based external pool. On both, I run VirtualBox. On one where the VirtualBox machines are stored on the builtin APFS volume, everything runs fine. But on the other where I store the virtual machines on the zfs pool itself, I repeatedly see kernel panics within VirtualBox. I thought initially these panics were due to a bug introduced into a recent version of VirtualBox, but going back to older versions doesn't prevent the panic. It's now looking more likely this bug originates in zfs and it may have been introduced in a recent version of it. (I think I'm running 0.90).
This panic occurs frequently enough that it is testable.