as Dan stated its not like Java is totally unusefull for games but its still has its performance issues if you build something bigger
indeed the ouya is far more powerful then any tablet so this might not be a problem for any well optimized game, but if you plan to publish your game on some other android plattforms native code would provide you a bigger, or better more satisfied, audience

im very interested in what we will see in the ouya store after the offical release, as for now i heared there are alot of quick ports from smaller android games. some gameloft style HD games would be awesome and a it would be way cooler if they come from indies and not from the big developers (like gameloft)