I use my Stock Thunderbolt to tether laptops (Windows, Linux) to and it works fine - the computer sees it as a bluetooth modem and all is well.
Android, and in particular Jelly Bean, has a problem with Bluetooth Internet. It works, but some of the applications that use it do a check for mobile connectivity and WiFi connectivity and don't bother checking Bluetooth connectivity.
So those applications that simply use the Internet connection and return a failure if they cannot connect work fine. Ingress runs great on my Nexus 7 tethered to my Thunderbolt.
Those applications that check for the two most common connection types and don't even try to connect to the Internet if one or both are not present will simply not try to connect to the Internet, and they'll fail, unaware that all they have to do is make a connection request and it will work just fine.
Unfortunately, Gmail and most of the Google services fall under the latter category. In fact, even Ingress shows a big red NO DATA CONNECTION error in the corner, even though it plays just fine.
If you want WiFi tethering, you'll have to replace (or have an app replace) a Gingerbread system library with one that allows third party WiFi tethering, and to do that you need root.