there are MANY reasons why a module needs to have a 'closed source' component
Not a single one. Unless you like to play The Gimp in Zed's Basement.
Also, "regulation" doesn't work by "closing source". It just doesn't. If the FCC "demands it" (haven't checked), the FCC is full of cluless idiots doing Broadcom's bidding (oh surprise!)
If you want "tamperproof", well, you better have the appropriate chip on you board. This is known as "trustworthy computing", i.e. trustworthy from the manufacturer side while the user gets an additional bell on his collar.
So if you can re-compile the kernel and the ZFS module for the new kernel, there should be NO issue with the GPL.
Your personal interpretation of the GPL is well noted.