My recommendation would be not to bother about the reservation, to just come down and check out all the hotels in Bayahibe one by one until you find one that is of your liking. Finding a room should not be a problem.
On a recent trip to Bayahibe we did so and overnighted in the first hotel coming down the town's main street. After checking out all the others it was the best. We had to accept intermittent water service -- a rooster who got to work at 5 am outside our window, but for a place to spend a night it was clean and the beds hard enough. We were a group of four rooms amidst family and friends so we used a diversity of rooms at the two floor hotel. The price is very very cheap, so you get what you pay for.
More pricey hotels are located in the Dominicus area, near the resorts. There are some small hotels there, too that you should check out if you are in the area. The Dominicus public beach strip, adjacent to the Dominicus Palace, is the best in the area. There are hotels that are walking distance to that beach strip.
Bayahibe was a good option, too, although would recommend you avoid it on Sunday because the beach may be too crowded and loud. We dined under the stars in Bayahibe and walked all around the town. It was a great weekend for the family.
