You probably need some sort of driver (System Extension). I got a USB 1.0 card once for a PC I used to own. Sat around for years as I killed the PC, until I got an OS9 Mac with PCI slots. I had to hunt down drivers because the card was not recognized under OS9. Once I found some extensions and installed them the card was recognized and that old PowerMac 6500 I have can now use USB.
I'd start your search with a Google search for "OS9 SATA system extensions".
After giving the highly recommended Intech speed tools disk driver a trial - without success - I believe it is the PCI rev2.1 -limit of the beige G3 which prevents the Sil3112 card from being detected.