Yeah san francisco de macoris has alot of diversity, the mountains were mostly afro-indegenous as the spanish component has been a later arrival post 1800s.
Yes there are "borrowed" words as you say, if it was only a few dozen then it wouldnt be any different from argentinian spanish, but were talkin about hundreds if not thousands of words. Also dominicans say "como tu ta" instead of "como ta tu" the tu is before the ta, something not present in any other country i know of, and this is also an african trait, similar to how jamaicans saying "me a go" instead of "i'm a go". If you listen closely to the Andean accents, specially Peruvians, Ecuadorians, Bolivians and South Colombians u will notice they sound HIGHLY indegenous, they almost sound like native's who are 1st or 2nd generation learners of spanish, i have a hard time understanding quechua spanish as it is vastly different from dominican spanish.
About spain having some of these dialect features, well Spain's whole southern part, had not only moors and jews but also "sub-saharan" africans, specially post 1400s when Portugal sold hundreds of thousands of Africans to spain, mainly females that were used as maids. Cordoba, and all of Andalucia was highly influence by Sub saharan African, Jewish, Moorish and Gypsy customs. The canary islands was also a pit stop for enslaved africans to the new world, in the same way Cape Verde was a pit stop for the portugese.
I would like to find recordings of these manifestion of Arawak, or Afro-Arawak languages that have survived in D.R. Katherine Green is one ofe the people that have recorded this, but i have had trouble getting in contact with her.