It is connected through USB - standard HID device, no drivers needed.
I also tested with Unity 5.6.0f3 and the behavior is the same. I don't think there is anything that can be done. Others have also stumbled upon this:
http://answers.unity3d.com/questions/351141/joysti...
Alas there seems to be no solution.
Anyway ... I've hooked my RC transmitter through vjoy so I'll use that.
Best~