I've used 3Ware (only 4-port) SATA cards on Windows, Linux and Xen so I can't comment on specifically OpenSolaris. I have yet to have an issue with them yet. The 8-port 3Ware 9650SE-8LPML "officially" supports OpenSolaris 2008.11 as stated here. I realize the versions aren't quite a match, but I can't imagine it being too much of an issue unless 2009.6 is has changed radically.
You should also specific what bus (PCI, PCI-X, PCI-e, etc. etc.) you plan on installing the RAID card as different RAID card vendors tend to put different features on different buses. For example, 3Ware supports RAID 6 only on PCI-e x4 for 8-ports or more.