I'm not sure what the utility you're using requires, but I know when I was using my Bluetooth phone as a modem (DUN..it was a few years ago..
), I had to bind the device, using rfcomm.
Try something like:
rfcomm bind 0 <your bluetooth MAC addresshere> 1
And check out the man pages for rfcomm. You should wind up with a /dev/rfcomm0 device. Your utility will have to look at that device. The USB cable was probably coming up as /dev/ttyUSB0 or something similar.
Just a suggestion.