There are 4 dance clubs within 100 meters of each other directly on the beach in Cabarete..walking distance from most of the hotels in Cabarete. There's only one place (Ojo) that plays all Merengue and Bachata (and Salsa) but that's only Thursday night...the rest of the time and in the other clubs it's a mix of dance music from all over...
Sosua has several dance clubs, but 90% or more of the women are working girls...plenty of cheap hotels though and you can walk everywhere very safely.
Puerto Plata has many Dominican style dance cubs but they aren't very tourist-friendly...The tourist friendly spots are in Playa Dorada and not very "Dominican". To go to the Local spots you'll need transportation and taxis are expensive if your solo.
There are several "Tipico" type places with Dominican Music and Dominican crowds, but you wouldn't want to go there solo on your first trip to the DR. There are lots of great people, Foreign and Dominican, who will gladly hang out with you and take you to other clubs/bars that they're going to...
The Colonial Zone is plenty safe for a single guy and there are many clubs and bars with Dominican Music, you can walk from your hotel to the various clubs and restaurants without problem...there won't be many non-Dominicans out at night though....maybe 5%, so it could be kind of intimidating.
The rest of Santo Domingo has 100's of clubs, bars, Tipicos, etc, but rquires transportation and is definitely not very tourist-friendly at night.
Santiago has about a half-dozen trendy type clubs, and dozens of Dominican music dance clubs, but you'll need transportation (cabs are fine and cheap), and it's less intimidating for a single foreign guy than SD (IMO)...