A reference you may want to look at is "Rebel Watchdog: The Confederate States Army Provost Guard," by Kenneth Radley, (Baton Rogue: Louisiana State University Press, 1989).
Provost Guards were not always units that were dedicated to the duty full time like Military Police companies are today. Men, companies, and sometimes regiments were detailed to perform the duties of the Provost Guard temporarily. These duties were but not limited to the enforcement of the conscription act, shipping control, prevent straggling while the army is on the march, vice control (gambling, drinking, and brothels), deserters, Prisoners of war, movement pass regulation, and arrest and detention operations.
I hope this helps. Please let me know if you have any questions.
Respectfully,
Gerald D. Hodge, Jr.
War Between the States Historian
Historian: 39th Georgia Volunteer Infantry Regiment
http://39thgavolinfrgt.homestead.com/39thHomepage.html