the CDDL is not compatible with the GPL period.
this means that you can't take CDDL code (ZFS) and include it in GPL code (the linux kernel)
until sun changes the licensing of ZFS to be compatible with the GPL there is no way to
integrate the two.
there are portions of ZFS that have been released under the GPL (enough for GRUB to be able to
read files from it), but most of the code has not been.
the only people who can fix this incompatibility are at Sun.