Oh Yeah, This Will Cause Quite a Stir
Since unless you look like a doper hippie trouble maker (or an evangelist) there is a 0.000000001% chance the subject will come up (e.g. whether you even HAVE a return plane ticket) when you go to passport control, then I'd not worry too much about it. They have a tax system to collect on the overstay that is only RD$1000 after 5 YEARS staying beyond your tourist card so it is not great concern compared to other countries. Six months I think is like US$4 or $5.
Tip: At Passport Control don't let on you know a word of Spanish, thus no conversation will ensue. OF course if you look like Thalia they might assume you do.