i am using my Galaxy Tab 7.7 with Android 4.1.2 and it works fine with your android-rsap app and the VW FSE Premium of my Golf VI.
Also the DUN Plugin works without problems.
I also use a Galaxy S4 GT-I9505 but this is not as easy as my Galaxy tab:
The Galaxy S4 is using Android 4.2.2 and i can not use your great rsap app.
The connection between Galaxy S4 and VW FSE Premium is possible because the S4 support bluetooth rsap out of the box.
If i want to use internet on the S4 while the phone is connected via rsap to the VW FSE Premium i need a DUN client.
Using blueVPN it is neccesary to esatblish the DUN connection every time manually.
Is there a possibility to get a DUN Connection which automaticaly start everytime bluetooth connection is established?