I'd love if simulator would run on IOS devices like iPad pro. It's a powerful device with great display.  You may be right with the assumption that IOS still has very limited support for hysical controllers. - and Bluetooth is not an option for FPV due to time lag of bluetooth devices. This time lag is technology instrinsic. But there is a dongle available for a Frsky radio transmitter which may work. Could you evaluate this?

FrSky XSR Sim - USB Dongle Simulator

Thanks, have you tried that controller yourself, is it good for FPV? I guess both analogs nubs are self-centering like on most gamepads.

I know some people are successfully using it on MacOS. 

FPV Freerider is not available for iOS (iPhone, iPad)