i think in order for OS 9.x to see a HDD it has to have the OS 9 HDD drivers on the HDD.

do a format wile using OS X's disk utility and make sure you have OS 9 disk drivers selected before you format to see if that is your issue.

you could always try to hold option on boot to get to the OS selection screen and choose OS X to boot from. i cant remember if it allows volume booting or folder booting on a B&W G3