We are giving away Unity prizes because these communities are mainly using that engine, but we allow any engines / frameworks to be used in the jam. If you are using a non-Unity engine and you win something it's up to you what you're going to do with it (whether you're just gonna throw it away or give it away to someone who does use Unity).
Also, I think the bigger reward for winning is that you won, your game out of hundreds was chosen as one of the best ones, but just my opinion :D