September is traditionally the month when most hurricanes hit the Caribbean region. In fact, in 100 years, only David has hit outside of September (and that was on 31 August). We have yet to have a hurricane in October or November, but last year there unusually were two tropical storms, one in October and another in December. See
DR1 - Hurricanes
No one can forecast weather in October this far in advance, outside of generalizations. Chances are in your favor of good weather.
For an overview on weather in October, see
DR1 - Weather
One of the best sources, if not the best, on weather regarding the Dominican Republic is at
Weather & Beyond - DR1 Dominican Republic Forums
There DR1 experts and those who live in each area report back on the actual weather and forecasts for any storm that may affect this area.