The Initiative 502 booth at Hempfest 2012 was staffed by a college voice student who exhausted his vocal cords in raucous argument with potheads who felt that the legalization measure was a sellout of the medical marijuana industry. The same voice will be heard, this time singing in harmony, at 9 o’clock Wednesday night on NBC-TV, as the New York-based “a.squared a cappella” singing group appears on The Sing Off Holiday Special.