the Spanish you hear on the Dominican news, or spoken by politicians, or public speakers for some public occasion will vary DRASTICALLY from what you will hear "en la calle". I suppose this is something that happens in almost any language, but I've noticed it in Spanish, more so than most, and all over Latin America.
It's always best to learn proper Spanish, and then integrate slang, etc as needed. IMHO anyways.
"Culto" Spanish in countries like the DR, Cuba, Venezuela, Colombia, even Mexico sounds almost identical.