This is the G3 that still uses scsi for the HD, right? And I assume that your internal HD's mount fine... I can tell you why the scanner doesn't work - there aren't any drivers for it in X. In fact, NO scanner works with X yet... now that Photoshop has been released for X, that should change soon. The same is probably the case for CDRW drive, depending on the brand, or it could be that the CDRW drive won't work with your scanner attached... you might want to check with the drive manufacturer to see if they have released any updated drivers for it. Also... are you using the built-in scsi or do you have a pci scsi upgrade card? Some scsi upgrade cards do have problems in X, and I would expect that at least you CDRW drive would work under X.
And the reason why SCSI Probe won't work, even in classic, is because Classic doesn't handle any of the communication with the hardware. X acts as a "mediator" between the Classic Environment and the hardware, so any classic software that is depndant on direct hardware communication probably won't work.