Currently giving this a try. Note that OMV creates a rule to override the scheduler to `bfq` for all rotating disks. Since all 5 of the HDDs are participating in my ZFS pool, I simply changed `bfq` to `none` in `/etc/udev/rules.d/99-openmediavault-scheduler.rules`, then ran the following to apply:
$ sudo udevadm control --reload-rules
$ sudo udevadm trigger --type=devices --action=change