We have a two year boxer and have traveled with him three times (Cabarete, Pedernales and Salinas), but we have always gotten permission first. The smaller hotels may accept him if you email ahead. The resorts will not take him (all-inclusive). I would check out some place in Samana, because there are many French owners there, and French people are more open to dog-lovers.
My recommendation would be to find a good kennel and leave him at home if you will only be traveling for a week. While you may find a hotel, the problem is that you will be very limited in where you can go to eat and travel, and the dog will suffer from the flight.
Boxers look like pit bulls so everyone is scared of them.
We love our boxer, Mr. Jay, so understand your wanting to bring him along.