Ive looked into every variable in the GamePad class, there don't seem to be any way to know the controller type.
I tried haxxing the problem by using SharpDX to read all the controller names. But the index order is not always the same on the built in GamePad and the SharpDX result.
A haxx that could work is to wait for a press START input, and then see if any of the SharpDX controllers get the same input, at the same frame.
This could be something worth suggesting as an update.