One of the great things about using consumer video cameras at a wedding is to get well wishes, stories, and comments from guests. You can create a great video storybook just from the clips you get.
Be sure to have your video shooters move the subject to a spot where the light is going to be on them, not behind them. Otherwise you’ll have someone in the dark and poor video quality. Usually it is as simple as turning them 180 degrees so the natural light is shining on them. If it is late at the reception and it is dark outside try to go to a well lit location to get their funny story. Plus it will usually be in a quieter spot and better for the audio.
Don’t worry about it too much. It’s more important to get the videos than being overly concerned with the lighting. The bride and groom will appreciate that you where able to get the memory for them more than how well they can see the subject.