Sorry about that; I guess I wasn't clear before. There is a setting in the global.conf file that sets the permission required for a proctored set to appear in a student's list of sets. This is in the %permissionLevels hash, around line 630.
I now also (finally) have some documentation for the GatewayQuiz module on-line in the WeBWorK2 Wiki. That's at http://devel.webwork.rochester.edu/twiki/bin/view/Webwork/GatewayTesting.
Please let me know if this doesn't make sense.