Other than one house which I saw with an asphaltic membrane, every attempt at waterproofing roofs that I've seen in DR involved painting the surface with some elastic coating type product.
Out of curiosity, I took to Google to see what options were available for this task, and found some interesting info. Some involved membranes, some involved a sequence of painting with various coating products, others involved a combination of membrane and coating products, and the one that I found most interesting involved products by a Canadian company called Xypex. They offer various products, but basically, they all work in the same manner. They create a chemical reaction to form a crystalline structure within the naturally occurring pores and capillaries of the concrete, which in turn seals any path for the water to penetrate the slab.
The concept sounds interesting, and different discussions which I came across on the web point to the product being very effective. It would be interesting to see if this product or an equivalent is available in DR, and what the experience/results with its use has been.