There are some description values in DirectX that drivers return. For example MOUSE, KEYBOARD, JOYSTICK, GAMEPAD, DRIVING, FLIGHT. There are loads of other values such as DUALPEDALS, REMOTE and LIGHTPEN so as long as the driver describes itself correctly, DirectX (and you) know what the controller actually is.

But they all return data in the same group of axis, POV and button data. How the data is actually stored there is up to the driver. Some gamepad drivers that return the DPad data as axis, some as POV and some as buttons!

I'm guessing for a wheel it returns 32767 when centered but behaves just like a thumbstick - the further it is moved the more that value alters. Full left would be 0 and full right would be 65535 with lots of values in between.