Here is how I bluetooth tether between the prime and the HTC Thunderbolt (neither are rooted).
I have PDAnet 3.5 on my Thunderbolt. I have FoxFi on my Thunderbolt.
I have PDAnet Tablet on the Prime.
Start PDANet 3.5 on the Thunderbolt. Selecting the Bluetooth DUN button brings up FoxFi. Activate Bluetooth DUN on Foxfi. Configure the first time on PDANet tablet on the prime, then connect.
Browsing works, youtube works, but exchange email does not.