I expect those issues to be resolved before 16.04 is released. Even with those fixes, the interactive installer doesn't support ZFS yet so you will still need to drop to a shell to actually setup your zpool and your partitions.
[1]: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1527727...
[2]: https://bugs.launchpad.net/ubuntu/+source/zfs-initramfs/+bug...
And also has native support for ZFS, btw.
PC-BSD's installer understands ZFS. It creates an all-ZFS system, including the root volume. The boot manager uses ZFS for "boot environments".
* http://download.pcbsd.org/iso/10.2-RELEASE/amd64/docs/html/i...
* https://www.ixsystems.com/whats-new/2013/10/31/the-revamped-...