That's wrong, and misses fundamental information about the CDDL.
First, the CDDL gives absolutely no fucks how you licence a resulting binary. It only cares about the specific covered source files, and doesn't care what you bundle them with. So nobody would ever argue that the module should be licenced as CDDL.
On the flip side, you'd have a really hard time arguing that the module should be licensed as GPL.* Sure, there's maybe a GPL wrapper, but lots of modules are non-GPL even when they might feature such a wrapper. ie. nvidia. You also can't argue ZFS is a derived work of the kernel, which is really the crux of the issue. ZFS was first written on solaris, developed for several years on freeBSD, and remains neutral across 3-5 different supported OSs. There's nothing to indicate the GPL should have more claim over ZFS than the wrapper.
The one and only place you'll ever run into trouble is if you start trying to distribute ZFS *source code* in the kernel source tree, as a fully integrated part of the kernel. (EDIT: or compiled together in a single kernel binary, from said combined source) The CDDL doesn't care about the mixing but the GPL does. Literally everyone agrees this is a bad idea and nobody does it.
*Let's ignore for a moment for the moment that you *couldn't* since the GPL requires complete corresponding source code and you can't relicence the CDDL source code files.
> On the flip side, you'd have a really hard time arguing that the module should be licensed as GPL
That is the very thing that some people do argue, for example the sfconservancy people. As I note, canonical's lawyers take your view (and I personally agree), but it's not clearcut. The sfconservancy outline their reasoning clearly for why they think zfs.ko is a derived work of the linux kernel.
Their stance isn't just rejected by nvidia and company, but also by the kernel devs most notably torvalds himself.
Torvalds himself has personally refuted the "linking inescapably means you're derived" point on multiple occasions, and yet here they are continuing to wave it around because that's how they wish it worked.
Does it change any of the other information? I admit I shouldn't have written "both require the entire derived work to be distributed under CDDL/GPL", and instead should have written "both may require, depending on a court's interpretation, the zfs kernel module to be distributed under CDDL or GPL respectively".
I think the rest of the comment stands though, right?