It will stress the driver to the breaking point with massive I/O operations. It will pummel your typical RAID controller CPU and cache. It's quite possible that at some point the driver support will actually be up to snuff, but ZFS is *incredibly* demanding. I am sorry that Avago has chosen to mislead people by trying to market this card as a multimode card. If "storcli" runs you have the wrong product. You really need the true HBA product and it needs to be in the software-RAID-bludgeoned-out IT mode. The 92xx and 93xx controllers are definitely known to exhibit issues under ZFS-class loads. It really needs to be as close to 100.000000% perfect as possible. ZFS can pound continuously on your controller for days doing a scrub or resilver.
These things do have drivers for FreeBSD, but they're really oriented towards typical "run a program, write a datafile" style usage. There's a lesser number of hours on the 12Gbps HBA products but they're known to work with only a caveat or two. There are billions of driver-hours of FreeNAS on the LSI 6Gbps HBA 20.00.07.00 in IT mode and all the bugs are shook out. Even if there were, there is still the issue of driver support. It is a hardware RAID controller, and there is not an option to omit the hardware RAID data path. It might be an "'HBA'" but it isn't the HBA we need. No, you cannot switch the personality of the controller to make it act as a true HBA - not interested in arguing the point, it's just a fact.