nvidia is using parts of the Linux API that the Linux developers have explicitly declared to not activate copyleft. They have at times asked for more non-GPL APIs, which I think has been denied:
I don't know what the situation is with ZFS with regards to the APIs that it's using.
There is also the question of how the software is being combined and distributed. If you receive ZFS and Linux as a "single work", which in SFC's view Ubuntu is doing by putting it all together in a neat little binary package, then the copyleft might activate.
http://linux.slashdot.org/story/12/10/11/1918251/alan-cox-to...
I don't know what the situation is with ZFS with regards to the APIs that it's using.
There is also the question of how the software is being combined and distributed. If you receive ZFS and Linux as a "single work", which in SFC's view Ubuntu is doing by putting it all together in a neat little binary package, then the copyleft might activate.