Bummer, prepped a group of 3 iPads on Friday and experimented with them today. Pushed apps down through my MDM, but not silently, as it asked for the password... I expected that, but strangely I could hit "cancel" and the apps still seemed to install successfully on two of them (maybe because they've been on those iPads in the past before I wiped them?). The third iPad acted more normally, with the app failing to install after I hit "cancel".
I also tried pushing a different app that I know had not been used on any iPad associated with the Apple ID I'm using for the test, in case this was skewing my results... This time I was prompted for a password on all 3 iPads, and hitting "cancel" prevented the installation on all 3. So I guess I don't even know what to make of the seemingly random results I get whenever I try to set up a bunch of iPads all the same.