Due to an NFS Bug, when ZFS is shared over NFS4 on the client side all files will appear owned by nobody:nogroup. If idmapd is not set it will be 4294967294: 4294967294.
The client can still read and write and the files will appear normally on the server. Chown will fail, which means you cannot run VM images off this share.
Mounting this with nfs option vers=3 in /etc/fstab is the only workaround until the bug is fixed.