Never had to arrest any Puddle Pirates myself!
"Scout" is just the name of a class. The Spencer Carbine is considered a Milspec weapon, and can be shot in the Milspec classes. Indeed, I reccomend shooting the Spencer in the Milspec Black Powder Repeater class, as the Spencer is virtualy the only MBPR we have available, thus MBPR (Or Black Powder "Marksman" under the new class names) is a Spencer class.
You do not have to wear a uniform to shoot in any of the Milspec classes. Nor do you have to dress like a Scout to shoot in the "Scout" class. Classes are defined by the rifle you shoot, not how you dress.
An authentic "Scout" portrayal is very welcome, no matter what class you shoot.
Though I mostly shoot a Krag, over the years I've accumulated a Spencer, A Trapdoor and a Sharps myself. My son will be using the Trapdoor at our Departmental Muster in July.