Jim:
The queues used by QMSS should be thread safe, I wouldn't worry about using a semaphore. You can read up a bit more on this in the Multicore Navigator User's Guide available here http://www.ti.com/lit/ug/sprugr9f/sprugr9f.pdf.
Chapter 4.1 discusses the registers associated with the queues and their atomicity. You can jump right to there or search the document for "atomic" to find more information.
Sincerely,
John Demery