While both side of the Galactic Civil War were happy to hire people to help the cause (hey, that's how Han Solo got started in things), it's mostly associated with the Empire. Well, The Bespin Gambit expansion for Imperial Assault has several Mercenary figures available in it. So no matter what side your on, if you want a little boost to your army, you could use them.
In this new set, the story is that there's a spy missing in the city. Both sides want to get to them first. There's all sorts of information they might have that could help (or needs to be covered up). To get around the city easily, you could make use of the Cloud City Wing Guard. Or perhaps to get into some of the dark and grittier areas you'll hire out an Ugnaut Tinkerer. Either way, they can help you track down that spy.