Hello
It is EXTREMELY HARD for a cuban national to get a Non Immigrant Visa in your case Visitors Visa.The US Govt has made it a point NOT to issue Non Immigrant Visas to Nationals of country they consider to to sponsor terroism in this case Cuba.They Make this fact public.
If the Cuban National does convince The US Consulate in Santo Domingo that they have VERY STRONG TIES in The Dominican Republic such as a House,A good job,savings,children,savings,and a very good reason to visit the USA and the consulate approves the Visa..The Cuban National must then wait for special approvement from the State department that could take 4 to 12 weeks.I have seen cases of Cubans who were approved by the Consulate but then denied by the State department.
Its Ironic and stupid in my opinion but its easier for a Cuban to enter the USA by Mexico or by sea and claim Automatic asylum than it is for them to recieve a Non Immigrant.
US Authorities tend to be even more supicious of Developing country nationals living in other Developing nations trying to obtain Non immigrant visas for the USA.
I would suggest that unless this cuban is well established in the Dominican Republic and has strong ties there to save your money and energy for something else
Good Luck!