I agree with Quisqueya, except for the bit quoted above.
Dominican Spanish is not
a patois. Although Dominicans have a distinctive accent and some borrowed vocabulary from African, Taino and English languages, it is comprehensible to all Spanish speakers everywhere. The same cannot be said about Creole/Kreyol and French speakers. All the non-Haitian French speakers I know who have learned Creole/Kreyol have had to approach it as a new language. I can follow a conversation in French and even participate a little, but when it comes to Kreyol I can only identify a few words because they sound like their French counterparts. Creole/Kreyol and French are much farther apart than the form of Spanish spoken in the DR and the form of Spanish spoken in Castilla.
The literal meaning of 'Castellano' is the Spanish spoken in Castilla (central Spain) but has now become synonymous with any sort of Spanish. Many Latin Americans refer to the language they speak as 'castellano', not 'español'. One such example is the Argentinians, whose Spanish is very different from the Spanish spoken in Castilla.
In fact many Haitians would also say that Kreyol is not a patois, because they consider it a separate language.