In my experience, the only time Playa Sosua is rough (and it can of course get very rough) is when the wind is on-shore (that is from the North, usually with a bit of West in it) and greater than 6 knots. It also needs to have been persistent, blowing for a few hours (usually that means overnight).
Checking the waves at Cabarete shouldn't tell you a lot (unless they're really ferocious) because of the offshore reef. That of course is one of the features that makes Cabarete an ideal wind-sport site.
If waves are breaking over the seawall on the Malecon or on the cliff at Casa Marina, I'd say it's a no-swim and no-dive day in Sosua or anywhere on the North Coast.
That's the observation of a sailor (ex-sailor now).