It depends. The old style MC cable armor is not listed for bonding but there is a new style MC that does use the armor for bonding. AFC calls theirs "MC-Quik", designated as type MCI-A. I assume there are other manufacturers by now. It can be identified by the large bare aluminum conductor right under the armor. This conductor is just for bonding the wraps of the armor and does not need to be terminated in the box.
http://www.iaei.org/magazine/2006/09/new-form-of-mc-cable-crosses-application-boundaries/
