Fulcrum on Android does work with external Bluetooth GPS devices. It requires a separate application to interface with the GPS and provide the operating system with the location data.
The following steps should be similar on other apps, but you may need to consult their help documentation on how to connect to the external GPS and then override the internal GPS.
First, install the Bluetooth GPS app from the Google Play Store.
Then pair your GPS with the Bluetooth GPS app and make sure it’s working.
After the Bluetooth GPS app is setup, you need to enable “Mock Locations” by checking the “Enable Mock GPS Provider” in the app.
This will open the Android system developer settings where you can check the “Allow mock locations” setting.
Once the Mock Locations setting is enabled, Fulcrum should now read location data from your Bluetooth device.
If you can’t find the setting, follow the instructions here for enabling the Developer options for your device.