This may be coming up more often. We just returned to DR and were asked to prove we had residency or return ticket by AA.
But someone else on this site already offered an easy, simple solution. Just purchase the "great deal" ticket to get to the DR as a one-way. Then purchase a return ticket separately, but buy a fully refundable fare. Once in the DR, cancel the return ticket and get all your $$ back. Then, when you are sure of your return date, shop for another "great deal" one-way return ticket.
Any problems with the above plan that I didn't think of, other than being out some $$ for a week or so? That is cheaper than paying airline change penalties.