You are obviously suffering from what they call in general aviation "go fever." You are planning to do something under marginal conditions (see JFK Jr.) and you know you should just stay home, but you really, really want to go. You have asked the correct question, but despite what almost everyone is telling you, you're still saying "but it's only a broken rib."
Here are some good questions for you:
Do you have trip insurance? Most people get it these days and injury or illness is covered under most plans. If you have insurance, use it and go another time.
Is the possibility of a pulmonary contusion or pneumothorax an acceptable risk for you and or your family to take while on vacation?
The Dominican Republic is a place where proper medical personnel and facilities may be many miles/hours away. How far away is the nearest chamber? Do you have DAN insurance?
Have you called the DAN medline to ask a dive medicine expert if they think this is a good idea? I like SCUBAboard, but the right people to ask about this is your physician or at least DAN.
Look, we wouldn't be in this forum if we weren't all crazy about diving. But diving with a serious injury, especially an injury that could threaten the lungs is just plain crazy. Do yourself and your loved ones a favor and postpone your trip. Don't turn an annoying injury into a life threatening one.
Happy Diving!