I don't know the answer to all of your questions but I do know this. The US Immigration service has a lottery every year where people from countries that don't have a high percentage rate of being admitted into the US every year get a chance to get a visa. I know that the Dominican Republic has consistantly been ineligible for this lottery due to the high number of admittances from that country. I don't know what the percentages are of acceptance vs. non-acceptance but I think the fact that DR is usually on the lottery ineligible list says that a lot of DR folks are successfully and legally getting into the country each year.
