Indeed, but generally people seem to be coming at it from the Oracle suing over the CDDL side.
Additionally, if I understand correctly, in order to have a chance to sue, Oracle would have to show that the code in question violates their actual copyright, which is only in code that the wrote/contributed. So Oracle would likely need to prove that the ZFS code interfaces/touches/uses their copyrighted code, otherwise they would not have standing (in the US). I have no clue if that interaction occurs or not.
As Oracle has contributed to the Linux kernel as well, they are in a position to sue over GPL violation.