Is there a way to use my android device as a bluetooth USB dongle without rooting it?
If I understand your question correctly, you are curious if you can plug your phone into the USB port on your laptop and use the bluetooth connection of your phone as if you had bluetooth service on your laptop.
No, that is not possible. The USB drivers for your phone do not permit that type of functionality.
This is possible or not possible depending on what you want to do with the bluetooth. If it's something that an app on the phone can do, and you are willing to enable USB debugging mode on the phone and put the SDK's adb driver on the netbook, then you can indeed have the PC make requests over usb for software you create for the phone to do things with its bluetooth.
But if you want to do bluetooth things that applications (sdk, native, or poking around behind the scenes unsupported) cannot, then you are out of luck.