Install
I couldn't get ZFS installed via the OMV GUI. Instead I installed it directly via the terminal:
apt update
apt install dpkg-dev linux-headers-$(uname -r) linux-image-amd64
apt install zfs-dkms zfsutils-linux
Now, in the GUI go to System > Plugins and install openmediavault-zfs.
source: https://openzfs.github.io/openzfs-docs/Getting%20Started/Debian/index.html#installation
Configure
Go to Storage > zfs > Pools and add a new pool. I recommend setting the compression to lz4.
You now have a working storage pool set up.