I agree with most of the post, the issue you state seems more to be of character and agenda rather then ethnicity.
Why is she down there anyways?
Does she have job/internship there?
Is this an extended vaction/ infatuation /fling?
Who is paying for this Island Adventure?
Suggestions to the parents?
Easy....... play along.
Invite them to dinner/ weekends. Have Dad grill him about his finances, job, education, ambitions, social values, morals, RELIGION, polictical ideology, what type of wedding, where they will live, what the culture is down there regarding marriage, does he have health insurance, is he saving for retirement and what his plans are for retirement later in life, how many children would he like to have, will the daughter be able to be a stay-at-home mom or does he expect her to work, does he like football, can he BBQ, explain that marriage is sacred to their family and not to be entered into lightly. Ask why he thinks his previous marriage broke up (this will the most telling-if he totally blames her then he is a loser, if he takes responsibility then proceed with more questioning) Have dad tell him how precious the daughter is and have him make it clear that if someone was to use her or break her heart, well dad just doesn't know what he would do. If all this doesn't scare him off....then repeat again more or less two weekends a month. After all this person might become family. So of course the parents want to develop an family like bond with the young man in question. If the man is shady and looking for $$$$ 6 months or less of this will rid you of him. If he is looking for citizenship via marriage, it should come out when answering above questions.
Of course if this is all sincere then it must be accepted that there are always those who seek beyond their backyards and just as many who are content to never leave the theirs. (my spouse and I can find distance kinship to each other in 4 of our bloodlines but my parents after 12 years of marriage still refer to him as that/the "Cali-foreigner")
So see...ethnicity is in the eye of the beholder =same ancestors but different regions of the USA.....isn't that sad and hillarious at the same time!!!
Beyond that I would stress !!! birth control !!!