The A/D conversion is done by the d:vice. Apple's Lightning connector is digital only (unlike the old 30pin connector, which at one time was both analogue and digital, before it became digital only around the time of the iPhone 4S).
As well as the digital audio signal, Lightning carries power and control signals. So the DPA app can in theory set things like gain level and sample rate (it doesn't control sample rate at the moment). Other applications can also change these things, if the DPA d:vice and the 3rd party application use standard 'CoreAudio' functionality. The DPA app has a 'lock' button, which implies that the parameters it sets can be locked so that other applications can't change things. That would be a proprietary control.
It's hard to say how this will work in the real world without trying one.
As a similar example (and related, because Macs also use 'CoreAudio') - if you have an Apogee audio interface, the mic pre-amp gain can be set on the physical interface itself, and by the Apogee Maestro app on the Mac. If you have Apple's Logic (DAW) then you can alter the mic-preamp gain from inside Logic, but if you use Presonus Studio One, you can't.
Does that help? Probably not. We will have to wait to see..........
Dominic