From the FreeBSD Quarterly Status Report, FreeBSD’s boot loaders have a patch to support ZFS booting:
ZFS Support for UEFI Boot/Loader: UEFI-enabled boot1.efi and loader.efi have been modified to support loading and booting from a ZFS filesystem. The patch currently works with buildworld, and successfully boots on a test machine with a ZFS partition. In addition, the ZFS-enabled loader.efi can be treated as a chainloader using ZFS-enabled GRUB. The work on boot1.efi also reorganizes the code somewhat, splitting out the filesystem-specific parts into a modular framework. Open tasks:
1) More testing is needed for the following use cases: ZFS with GRUB+loader.efi, ZFS with boot1+loader.efi, UFS with boot1+loader.efi (to test the modularization of boot1.efi)
2) Have boot1.efi check partition type GUIDs before probing for filesystems.
3) Get patch accepted upstream and committed.