As far as I know iOS still has very limited support for physical controllers. I know some bluetooth controllers might work, but as far as I know it is not possible to connect an RC radio to iPhone/iPad devices, which makes it less appealing for a FPV simulator in my opinion. (Most people would just be able to fly using touchscreen controls, which is not ideal for FPV practice as I see it...)

If anyone has other information regarding physical controllers on iOS please let me know.