It has "official support" from the ZoL folks. And yes, openSUSE has ZFS packages in OBS. But we sure as hell don't ship them by default, or in our official repos. The same applies for Arch, Debian, Fedora, Gentoo, RHEL and CentOS.

Ubuntu is the only distribution that official supports ZoL, and actually ships it in it's official repositories (and by default). What that means is that Canonical is effectively saying "we trust there's no legal reason why we cannot do this." No other distribution has made that claim.

EDIT: Actually NixOS also supports it, but the point stands.

Well, also NixOS.

Supported by whom? Is it at the level one can expect from paid support from say Red Hat, SUSE or Canonical?

They're referring to ZoL providing support for distributions (which actually just means "it works, and if you send a bug we'll work on it"). Only Canonical provides support from the distribution side. See https://news.ycombinator.com/item?id=15088761.