If it helps, I was able to confirm that the DTC-100 (included USB dongle with the Luna) works with Android and USB Audio Player Pro by testing with my Cayin N6ii (runs android 8.1.0). This was tested with it connected directly via the USB-C port on the N6ii.
Upon connecting I am prompted as to whether I'd like to open USB Audio Player Pro or Neutron (the 2 current apps I have installed for this kind of thing). USB audio player pro seems to work perfectly with both local and streamed files. Tried neutron once and I can't get it to work, but I normally do not use it, and it very well could be an app/android configuration I have incorrectly set up (or conflict with UAPP? no idea).
Volume changes work as well with the hardware knob on the N6ii in UAPP. This is the only android device I have to test with. No idea about other android versions or phones/devices, but the DTC-100 seems to be very flexible in what it can be connected to (at least with the 3+ computers + iphone and now a DAP I have connected so far).
Edit: actually, the stock Cayin app and Hiby app also work with this for me. Specifically, this works with the DTC-100 as the output, while the DAP itself functions as the source, including volume knob...interesting...in the past when connecting to an external DAC (which did have an XMOS chip though), I had some trouble getting things to work unless I used UAPP...
Usually I leave the DTC-100 plugged into the front USB of my PC these days for an easy + quick DAC so my experience is also a little limited. Anyways, hope that helps!