I would expect the MOGA controllers would show up as standard controllers and would just work, but they do have their own SDK here: http://www.mogaanywhere.com/developers/
It works on my Note 5 and shield tablet, I originally bought a steel series for bluetooth controller testing but a friend bought a moga for his galaxy 7 and couldn’t get it to work, it worked on my device so we traded
I am using my I plugged in some event ticks to ‘gamepad right thumbstick X’. It worked in PIE on my controller, but not when I ran the build with my MOGA.
Make sure the controller is paired with the phone. If you watch the UE4 logcat output and press a button you should see a new device registered the first time. If not, the controller wasn’t recognized by Android with proper HID.