Before you drop $10,000 on a new RAID, you might wanna learn a bit more about what you are buying. If you say IDE isn't fast enough for your needs, I assume you are buying 15k RPM Ultra 320 SCSI drives, and plenty of them, in a very fast, expensive RAID controller. You won't be getting a "fiber-optic" one, however, but you could be getting a Fibre Channel one, like Apple's XServe RAID. In that case, Tiger wouldn't even NEED to support SCSI, as the hardware RAID controller will handle all of that.
How much throughput do you actually need? An XServe RAID can get 400MB/s, which seems to be enough for most anything.
Tiger DOES, however, support SCSI just fine.