Apparently Gears of War 3 was supposed to have special unlockable equipment and skins for those who had played previous Epic games. This would have included a special gun from Bulletstorm and a Shadow Complex gun if they had been able to implement these features. Unfortunately due to restrictions on the Xbox 360 itself, Epic will not be able to do this.
Epic Games lead gameplay programmer Joe Graf explained on his Twitter that the Xbox 360 will only read data from inside the publisher and developers own family. Meaning that Gears of War, which is published by Microsoft Games Studios, will not be able to access data from Bulletstorm which is being published by EA. There may be workarounds in the future but as of now these special unlocks are canceled.