Yes, that is how it is described.
Take a look at the Mishima “Police (Watchman)” career.
In the section description is stated:
Officially, all law enforcement in Mishiman territory is the responsibility of samurai known as magistrates, and there are different orders of these enforcers in each city and on each world where Mishimans dwell. In addition to the order provided by samurai, many communities of commoners may appoint watchmen. These individuals help tend to disputes and criminal matters that are beneath the attention of the samurai, and while they have no official power, their presence is vital for maintaining the peace.
So it is clear the the careers listed under this entry are for Mishima citizens only.
Primary Careers in the faction books are - unless stated otherwise - for citizens belonging to that faction only.