Sabayon isn't supporting ZFS as the root file-system due to the CDDL-licensed file-system being incompatible with the Linux GPL kernel
I am one of the developers who contributed to ZFS support in Sabayon 9. The licensing conflict prevented us from putting ZFS into the kernel binary. That made implementing ZFS rootfs support difficult. It was still possible, but it had to be postponed until Sabayon 10 due to time constraints.
Also, it is possible to use a ZFS rootfs with Sabayon 9. That requires doing an install, booting into a Live CD environment, doing a tarball of the install, reformatting and reinstalling from the tarball as you would install Gentoo. It is not a user friendly procedure, but it should work. I use it in Gentoo.