I may be corrected on this, or there may be an easier way but...
Using Exchange Admin, Expand the server you want the information on and highlight "Server Recipients". In the Lower left hand corner of the window, there should be something that reads "12345 Recipients". Then under the "View" menu, click hidden recipients, and the number should change to "1234 Hidden Recipiants". Add the numbers togeather and there's your information. You can subtract one for the free/busy if you want to.