NJCAA bylaws allow for member colleges to hold one alumni game/contest per academic year, per sport. In accordance with Article VII, Section 5.A of the 2015-16 NJCAA Handbook & Casebook (page 82), alumni games are not considered an official game/contest or a scrimmage.
As an example, in the sport of basketball a member college is permitted to schedule 30 official games, 4 scrimmage dates and one alumni game.
In an alumni game, all participants representing the alumni squad must actually be alumni of the program. In the case where non-alumni are brought in to complete a roster, the game no longer qualifies under the alumni designation and must be counted as a scrimmage or official game/contest on the sport schedule.