Shotgun mounted on the camera? Absolutely NOT! Try that and your audio will be both faint and sound like the vows are being recited in a metal culvert under the highway. Shotgun's are not "telephotos for sound," such things don't exist. For clear recording of normal speech even a shotgun mic needs to be less than 2 feet from the person speaking and aimed very precisely at their mouth. You're not going to be anywhere near that close to the wedding party with your camera during the ceremony. Yu might be able to set up a mic on a stand right next to the officiant but then you have to worry about the members of the party being properly on-mic. So how do you get a mic close enough for clear recording? In a word ... lav. A lav mic on either the groom or the officiant. (Or both. If you were shooting it for a feature you'd mic all three - bride, groom, and officiant - but mic'ing the bride is not so common. Or you'd cover it with a boom, but that's out for a real wedding.) To record, either a wireless transmitter hop to the camera or recorder or a portable recorder in the pocket of the person wearing the lav.