It can work.  If you buy a C-Dock or C-Dock II,  it has an embedded SCSI controller.  I used to use a DLT drive with my Dell for quite some time.  Additionally,  if you want to use SCSI devices while mobile,  there are several variant of PCMCIA SCSI controllers.  Lastly,  I know they exist,  but I have never used any of the USB SCSI controllers.

I already have a C-Dock ll, just couldn't figure out where I'd connect the scsi cable to this thing. 

There is an HD-50 connector on the back of the docking station.  As long as your DDS-3 tape drive is a narrow decive you are fine,  if your device is a wide device,  you would need an HD-68 connector.  If your tape drive enclosure has a Centronics connector on the back,  you would need a convertor or a cable which does HD-50 to Centronic50.