With the exception of the Darwin platform (Ultra 5 and 10) and some other new offerings--which use IDE--and the UltraSPARC III-based systems--which use fibre channel--all of Sun's recent desktop systems use some form of SCSI. Most provide SCSI-2, Fast SCSI-2, or Fast Wide SCSI-2 with internal and external connectors. The external connector for the latter is an HD68 (high density 68-pin), while the others use an HD50.
Beyond performance issues, for internally mounted drives the physical connection is the most important matter affecting compatibility. Older systems use a standard 50-pin SCSI connector with separate power feed, while others use the single 80-pin SCA interface. In all cases I've seen, converting the latter to the former yields a package too large for the system enclosure.
No particular drive brand or firmware is required: if it implements one of the SCSI standards supported by the system's interface, it should work...not to say the old SCSI voodoo is unnecessary.