I have a hard time seeing an Uslamer getting off world much to be a pirate, as opposed to a swoop ganger and so forth staying on the world, and I don't think it makes sense for a non-Uslamer to climb the ranks except in the course of the plot, if one is better suited to that role in the future. A lot of the platoon's culture has to do with the fight on Uslam. Even an Uslamer pirate just doesn't feel right in that Uslam culture doesn't seem really suited to it -- they're miners and the like, after all.