Hi,
Just to add my input, lightning port iPads can indeed use more than one usb at the same time with the right USB adapter.
I used to use my old SB3 and hard drive together all the time.
You need the Apple adapter and a powered usb hub.
I’ve written two threads in the previously one here and another here.
Have a read through them, all you need is in them and you will be able to access your controller and hard drive simultaneously.
Cheers. 
