Next time your pop your Crackdown disc in (and you are connected to Xbox Live) youll get prompted for a title update. According to what I am told, The update addresses several minor technical issues to ensure a smoother online gameplay experience and increases the number of ambient gang vehicles that populate Pacific City. That last one should held with the Repo Man achievement.
There ya have it. Whats up with any DLC? No details yetbut we should have some news soon in it.