Woe is you
Basically, your friend will have to prove to the US Consulate in Santo Domingo that he or she is going to return to the DR at the end of their stay. This can be shown with proof of a good job or lots of assets in the DR. It's sort of like "Ok, you say you are going on vacation to the US, prove to us you can afford it." It does suck, but the US takes the position that if you apply for a visitors visa, you are intending to emigrate illegaly to the US, and the onus is on you to prove otherwise. The Dominican Republic is #1 in US visa fraud world wide (US Consular Newsletter Vol.1 Issue 2 jan 1999)
If your friend is a woman, you will have further problems because the US will assume that it is your girlfriend even if it is not, and tell her she has to get a K1 fianc? visa. You have to sign up for that and sponsor her and go through a big ordeal. I am going through that process now with my fianc?. I sent the papers in May 23 and she will get her visa interview date in roughly 2 months (she just recieved what the US govt. calls "packet 3" yesterday!)
If your friend is some sort of professional in the DR you probably wont have a problem. They better have bank accounts in their name, preferably cars and property also. Basically they need to look like their standard of living would be lower here as an illegal than it is there doing whatever it is that they do.
I can give you some links to immigration and visitor visa pages if you want