Yes, all current MBPs have SATA III in the Optibay, but
OWC says this only works properly on the 13" model, even after the EFI 2.2 update. I don't know if this is the case for all SSD drives in the 15"/17" models, but If you're planning on putting an SSD in the optibay of one of these models it may be safer to get a SATA II SSD. Looks like SATA III on the optibay is not a problem for the 13" MBP, though.