In Visual Guard, are there DLL's that we would compile against containing the functions that would be called which in turn access the database?

Visual Guard has his assemblies(DLL) which you need to refer in your application, which in turn will access to VG database to perform action. This assembly also contains API which has tons of methods to communicate with Visual Guard features like CreateUser, UpdateUser, GetRoles, AssignRoleToUser, etc. Through API, you can explicitly perform action in your application.