I want to emphasize that the goal of our submittal process is to ensure that your submittal can be exactly reproduced by anyone, and that derivative works can be freely created if you are chosen as a finalist and your entry is released as open source software. That means a third party would not have to enter into any other license agreements or violate any intellectual property or other rights to do so, and they could modify your software to run on a different device. We're not trying to create technical obstacles, but we must ensure those goals are met. It's sometimes easy to overlook the details of all the things you did while developing your solution.
The most recent Submittal Instructions (v1.1) explain that the tablets prepared for judges will have Android 7.1.1 installed on them, and the filesystem images you submit will be flashed on to those tablets. Any partitions you do not submit will be left unmodified.
If, for example, you used a customized or proprietary boot.img during development or during tablet preparation but your entry does not require it, don't submit it. If you used the stock boot.img from Android 7.1.1 unmodified, don't submit it. You don't need to demonstrate that you can produce filesystem images which, when flashed on to a tablet, have no effect but to duplicate what's already there.
With respect to your two questions, then:
It sounds like you are asking if it's OK to submit an undocumented, irreproducible file that needs to be flashed to the boot.img partition. No, you may not do that. We would have no idea what's in that partition, we'd have no way to reproduce it, and we would have no information about where it came from. That would clearly be in violation of the intent of this competition.
It's not clear whether this is a different question. If you're submitting and would like to use a boot.img partition, you need to provide the tools and instructions to build it. If you don't do that, isn't this the same as question 1?
Feel free to give a more specific example if I'm not understanding either or both of these questions.