As I indicated in my post, I believe the best person for you to contact is the administrator of a good private school, an American school. These schools send students to the US and Canada to attend the universities. Very, very few graduates of the public high schools make it to universities other than Dominican.
I believe you will find that the good private schools have some sort of link to accreditation sources in the US and that they have met the requirements of these sources with respect to curriculum, faculty qualifications, etc. I do not think the accreditation comes from a Dominican body.
Additionally, the students from these schools that want to enter American institutions of higher learning take the SAT examination, which gives them a score that college admission people can use as a measure. Additionally, these schools have acquired a reputation over the years based on scores of students on SAT, percentage of students going on to higher education in the US and Canada, performance of these students in these colleges and universities, etc.
Again, I don't think there is a better person for you to contact than the administrator of one of these schools. I believe, as indicated above, that the accreditation of students will come from outside the DR.
I know of doctors that graduated from Dominican schools of medicine that went on to the US for further training. But they had to pass the appropriate examinations to be admitted.
I don't think a blanket statement can be made that a DR University Degree is not equivalent to a Canadian/US high school diploma. But it can be said that a degree from a DR university is not equivalent to a degree from a US/Canadian institution of higher learning.