I'm getting married at Dreams Cancun also and I decided to go with another photographer. When I first compared the resort photographer's work to other photog's I didn't think he measured up but I wasn't willing to pay the high cost of those better photographers.
After a stressful search I decided to go with Sascha Gluck, i like his work and he has good feedback, a good price, and was available on my date. I'm still using the resort photographer but will do a session the day before the wedding. I'm planning to ask our group to wear white while FI and I are in a color. I figured this way I get 2 sessions with 2 different photographers so I'm bound to get some good shots!
Actually after the resort photographer contacted me recently I was wondering why I stressed so much over it. I've seen some good feedback and pics from him on this forum. So don't stress too much over it but decide soon since the photographers book up rather quickly.