No, you have to buy the Epic Edition of the game. There are codes that come in the box.
But don't worry, if you don't want to buy the Bulletstorm Epic Edition there are multiple ways of getting into the Gears of War 3 beta. If you do decided to get it, you get a headstart playing the beta.
If you don't want to get the game, keep your ears open for when the other ways of getting into the beta are revealed.