A wedding DJ is responsible for the flow of the reception. He usually serves as the MC for the evening as well as playing the music. It's critical to meet with your DJ to consult with him/her on the timeline as well as the playlist. Communication is key to a successful outcome as well as avoiding any "surprises".
Wedding photographers typically work along side the DJ during the reception. The DJ should cue the photographers, letting them know before announcing the next element so they can be prepared. Vendors should always work as a team to produce the best experience for their couples which will, in turn, produce keepsake photos!