The only curiousity I noticed is that the ones I knew (from Para and Minas Gerais) may have a broader definition of 'white' than DR. But I still wouldn't generalize the entire country based on those individuals.
Now regarding the whole trendy nightclub scene, I have no personal experience except via others who have gone, here's my summary:
-Connections and socioeconomic class seem to be the common denomitor as to who gets in or not.
-I can google pics of crowds in these clubs, and I have seen people of obvious African ancestry.
-The sure way not to get in is looking like the stereotypical DomincanYork or a chopo. My barber is half-Italians and looks fully European but very stereotypical 'chopo' and was not let in to one of them.
This being said, I still wouldn't come to a definitive conclusion or generalize the entire country or its people based on what may or may not have been a factor in not letting some people in.
For example, there was an African American night club that got into trouble for having 'light skinned' nights and not letting in darker skinned people. This does not reflect the US or African Americans in general.