I believe that is correct, with a limit of 14 pitchers (rest of the season, it's 13).
The ability to move guys up and down all month is enhanced greatly by the change to the minor league schedules over the last few years. They used to end right about Labor Day, with their playoffs after that. Now, the AA season stretches until September 17 and the AAA season goes until September 24, so its not like the callups are sitting around all month.