What are you trying to tether to?
I just tested this out on my T-MOBILE HTC ONE & HISENSE SERO 7 PRO Android Tablet:
1) Install FOX-FI on the phone.
2) Install PDA NET for Tablets on your Tablet.
If you use BLUETOOTH MODE, you should be able to connect,as I am using my tablet to post this as we speak, using the abovementioned.
Gonna try it on my desktop PC, be right back.......