Sorry, I think I might have confused OmniOS with QubesOS.
ZFS is itself a security feature because of how well it guarantees the fidelity of your data. That said, ZFS support on BSD is generally much better than on Linux
For the reasons you stated, I can’t use OpenBSD on my daily work laptop, so I don’t think I will ever really have a chance to give it a fair trial or learn more about it, which is unfortunate.