Don`t worry! In the past 5-6 years here in Playa I only really remember one somewhat hurricane that was then downgraded to a tropical storm and that was in October. August is a great month to get married, it WILL be hot but everything will be just amazing no need to worry.
I would not worry about hurricanes at all for the Riviera Maya, the Pacific side seems to get most of the warnings but we are just sitting pretty here in Playa. Nothing to worry about!