Will the Lightning to USB 3 adapter let me connect via Xcode for debugging via the power passthrough? I see that the Lightning to USB 3 Camera Adapter has two 'inputs', the usb port and an additional Lightning port. From anecdotal evidence (I have found no official manual) it is for power supply. Nice, but. Can I use this port to connect to computer, for Xcode debugging purposes, while using the Camera Adapter for connecting a MIDI device at the same time? 

Thanks.
No, it is not possible. It can only be used to supply power to the iPad/iPhone.

The only way to connect multiple things is to use a traditional powered USB-hub connected to the single USB-port available on the Lightning to USB 3 Camera Adapter.