Do the Xi'an have a military?

Oh, yeah. They get tanks.

Every Xi'an, once they become a certain age, they have to sign up for the civil service, which is run by the Emperor's house, the Emperor's family. They do things depending on what their talents are and where they've been assigned. Some of them serve their stint in the military. Some of them join bureaucracy or other important government arms, but the military is big, and everybody essentially serves in it at one point in their life.