Oddly enough, ZFS support never made it into the next release of sys-block/parted. I dropped the ZFS patch for 3.2. After some tinkering to work around problems with the 3.1 zfs patch (because of added btrfs support in the automake files), it turned out the completely new libparted/fs/zfs/zfs.c requires some changes in calling internal functions.
3.2 is now stable, which means that 3.1 is not easily selectable in any branch any longer. Is there still interest in this Gentoo-added feature?
I added the Debian patch set in 3.2_p19, which includes ZFS support.