At the moment, there is only a hardware appliance (that I know of) that delivers real HA with ZFS from Zeta:
http://www.zeta.systems/zetavault/high-availability/
If you only want to access your ZFS (single node) from PVE over iSCSI, there is this pages that describes what's working:
https://pve.proxmox.com/wiki/Storage:_ZFS_over_iSCSI
As far as I know, a Illuminous-based ZFS is working, but there are also some other attempts to implement FreeNAS support as well as other nas-appliance stuff - yet not official PVE projects.
http://www.zeta.systems/zetavault/high-availability/
If you only want to access your ZFS (single node) from PVE over iSCSI, there is this pages that describes what's working:
https://pve.proxmox.com/wiki/Storage:_ZFS_over_iSCSI
As far as I know, a Illuminous-based ZFS is working, but there are also some other attempts to implement FreeNAS support as well as other nas-appliance stuff - yet not official PVE projects.