Ubuntu ships OpenZFS as a separate prebuilt kernel module for ZFS (zfs-dkms). Interestingly, they also have ZFS support in GRUB to support booting from ZFS:

  * read-only and minimal
  * fully aware of different Linux boot environments
  * GPLv3 license compatible, clean-room implementation by the OpenSolaris/Illumos team. The implementation predates Ubuntu’s interest.