Now I wonder if I can buy a SATA CD/DVD drive that will boot if I hold down the C key.
I'd say you've already demonstrated that at least with your particular SATA card no, you can't.
Per Trag's comment, Macintoshes do have a firmware function that you can access with the Startup Disk control panel, or that programs like the Tiger's installer manipulate, that sets a variable in Open Firmware that can point to a properly enumerated device on the OF device tree. That is why you *were* able to boot and install from the Tiger DVD after running the installer from Panther; devices on your SATA card are apparently valid targets for this mechanism and can be set correctly. However, since "C" failed you the first time it's a very reasonable guess that the firmware mechanism that looks for CD-ROM devices when you hold that down only knows to look for them on the internal drive controller's device sub-tree.
Assuming that's the case then, no, no SATA drive will ever work with that "C" alias. If you have some real need for a faster optical drive (why?) but want to retain the "C" booting option (instead of relying on having a working OS install that you can access the Startup Disk control panel) the B&W has two drive bays, you could always install two drives.
(Strictly speaking another option for cold booting would be to drop into Open Firmware with command-option-O-F and manually type a boot command that references the SATA optical device if for some reason you really needed to do a cold boot from optical. Figuring out the device tree entry is an exercise for the reader. You could also simply try holding down the Option key and see if the CD shows up on the graphical boot selector. I don't think any beige Macs support this but I think it's an option on the B&W. I have no idea if the "hold option" UI will find volumes on add-on cards or not.)