Using another phone's GPS signal as location
As a test confirmed, this is possible via corresponding apps:


on the device providing the GPS signal ("B"), you will need an app to Use your Droid as BT-GPS Mouse. An approved candidate would be Bluetooth GPS Output for this.
on the device where you want to access that "external GPS" from ("A"), you'll need an app to Use an external GPS mouse. Approved candidate for that is Bluetooth GPS.


As you yourself found out, another approach is tethering GPS with an app like TetherGPS Lite – which you write "sounds more efficient since it can be more optimized". As this waits your approval, please approve below this answer then :)