By now, it's well possible to get Ubuntu 16.04 running on a ZFS root-fs. Ubuntu 16.04 has ZFS in the default package manager, and with guides like this, it's not hard to get started.
However, all guides I've seen require being able to boot from a Ubuntu installation image. For a Hetzner dedicated server, this is an uncommon installation procedure, as it requires engineers to visit the server and plug-in a remote KVM.
By default, the dedicated servers boot into a rescue system, which allows to install a variety of Linux distributions through their 'installiamge' script. However, this script does not support ZFS yet.
How to get a Hetzner dedicated server running on a ZFS root?
Best Answer
The basic idea is to get Ubuntu installed on a small partition on the harddrive, partition the hard-drive to use the remainder of the space for ZFS, and then copy the installation over. I'm mainly using this guide on instructions how to do that.
Lazy, and experience with Ansible? I wrote a little stack of scripts to automate these steps. They are available on: https://github.com/tijszwinkels/hetzner-ubuntu-16.04-zfs-root-ansible/blob/master/hetzner-ubuntu-16.04.yml Be careful, these scripts assume that the host is booted into the Hetzner rescue system, and they will wipe your drives as a very first step. Use at your own risk!
Now, you should have a Hetzner dedicated server that happily boots into Ubuntu 16.04 with a ZFS root fs. Good luck!