Hi Susan,
We are getting married at dreams cancun a week after you, maybe you'll even still be there when we arrive! We decided on Claudia Rodriguez Photography Claudia Rodriguez, Photographer, Cancun & Riviera Maya, we are actually using one of her team members, Citlalli. They have been very responsive, there pictures are very good, and I thought there prices were reasonable. They also do video.
As for music, we are thinking of doing the IPOD thing as well, it is $180/hour to rent the sound system +10% tax. The DJ is more, I can't remember off the top of my head, but claudia did tell me if you needed the DJ for 4 hours or more she could get us a better price, but we haven't decided yet.
There are a lot of great photographers on this forum as well, some from mexico and others that you could fly in. It really depends on your budget. Elizabeth Medina is another great photographer from mexico, she's also a member here.