I to have done some time down there, good people abound, but not a MTB area.
MTBish without much driving - Bicycle Post Trails near Greenville, sponsored by bike shop of the same name, are your best bet, with some riding around Havelock, Wilmington and Fayetteville.
Road riding is flat but plenty of good county roads to chug out some hours.
And you are not far from some decent small swell surf on occasion.