I just played Dead Trigger 2. That is also made with Unity. It also is non responsive to media player buttons. Amazon should not be playing favorites and denying smaller developers for issues that larger companies are getting away with.
We are looking in to it. Pre-Submission Assessment Guide for Fire TV is updated.
https://developer.amazon.com/public/solutions/devices/fire-tv/docs/pre-submission-assessment-guide 3.5 Media Buttons Test: Press the Fast Forward, Play/Pause, and Rewind buttons. Expected Results: In media playback, the media buttons behave as expected. In non-media apps, the media buttons should not be used for some other function, as this may interfere with the system's ability to control media playing in the background. [b] Note that If your app uses a framework such as Unity, you may ignore this requirement , as the ability to pass key events through to the system is not supported in those frameworks.[/b]