Knowing anything about the military would tend to rule out special consideration. It may be that regimental commanders received orders to detail a certain number of men for this purpose, and company commanders had to pick from men present for duty. As to what factors guided these decisions, you can take it from there.
Konwing little about the shoe manufacturing process, I'm reluctant to add much more. However, it seems that tops and bottoms of shoes were cobbled together as the last step in making a pair of shoes. Made of different materials, it must have been a matter of fastening the two together. The process could be one of repair and restoration or new manufacture. In either case, the task would be a simple, repetitive process not requiring much skill or experience.