I wanted to have snapshots and installed just Ubuntu on ZFS using debboostrap - basically using the tutorial on the page here almost verbatim. Hetzner Cloud is not using UEFI afaik so you need to setup a small SYSLINUX setup to boot. But there is no ready cloud image for that. Another idea I didn't implement yet is to have a minimal image that I can bootstrap using send/recv but at the moment there's no need for that.