I was having problems tethering my Ipad 1 to my Galaxy Nexus through bluetooth. After quite a bit of tries with different apps, I discovered it is quite simple.
The Galaxy is rooted, and has minibox installed.
In Settings, under Wireless & Networks - choose "More", than go to "Tethering and portable hotspot", than check Bluetooth tethering. There are still simpler ways like using WiFi, but Wifi is a battery drain. So if you have to commute and have a long train ride, this is better.
Your Ipad has to be jailbroken. In Cydia search and install iTether. iTether is more than an app, it actually installs an alternvaitve Bluetooth stack that will override the one from Apple. Without this, the IPad cannot connect to other devices that are not from Apple.
Now pair the devices. On the Galaxy, go to Settings, Bluetooth screen, and within iTether choose Galaxy Nexus, and everything should work now. Unpair and Forget Device if the Internet service fails to start, and start this step over again.
My Galaxy Nexus is rooted, and my iPad 1 is jailbroken.