Keep in mind that Solaris ZFS does not have support for Intel's latest C602/606 chipsets for storage. Any SATA or SAS ports coming off these cannot be used for install or storage. The only way really to get good support with new E5 based Xeon systems is with external storage controllers or onboard storage controllers (since ZFS prefers HBA's to RAID's), like the LSI 2308. That being said, many of the new SAS2 controllers like the 2308 are having issues with lack of support in minor things. For instance, ZFS can't blink or locate individual drives in an Enclosure attached to a 2308 controller. It also applies random drive names and the drive name may not have anything to do with the bay its in (for instance it may assign c0td0 to Bay 4 and c0td1 to Bay 7. As such, for drive replacements, you essentially have to write down the serial numbers and the drive bays of all your hard drives down, and then add the drives one at a time while checking to see what name the ZFS system applies to it.
HCL's are a pain in the butt. But if you want a truly easily deployed system you best stick to it or you could be in for hours of extra work or you may not get a working system at all.