I am currently running Yosemite (10.10.5) per http://forums.macrumors.com/threads/2006-2007-mac-pro-1-1-2-1-and-os-x-el-capitan.1890435/ with OpenZFS I have had no issues what-so-ever with this setup.
When I run El Captain, everything works fine until I install OpenZFS, then I get a kernel panic on reboot with the message "Unable to find driver for this platform: \"ACPI\".\n"0/Library/Caches/.../IOPlatformExport.cpp:1665. Before I reboot I can import pools etc... and everything seems to run fine, it just seems to be an issue with rebooting.
Any help would be appreciated.
Note: this is with 1.5.2.