The first former North Carolina player to play basketball at any sort of high level professional basketball was George Glamack. After his career in Chapel Hill, Glamack played several years in the National Basketball League in the 40s.
However, if you want to be technical with it, he was not the first Tar Heel to play in the NBA. While the NBL was one of two leagues that merged to form the NBA, the league itself considers the Basketball Association of America to be it’s predecessor. It considers the addition of the NBL teams to be an expansion rather that a real merger.