Catalyzes the NAD(+)-dependent oxidation of UDP-GlcNAc. Highly specific for UDP-GlcNAc, does not catalyze the oxidation of the substrate analogs UDP-Glc, UDP-GalNAc, N-acetylglucosamine and glucosamine. NAD(+) + UDP-N-acetyl-alpha-D-glucosamine = H(+) + NADH + UDP-2-acetamido-3-dehydro-2-deoxy-alpha-D-glucopyranose Oxidoreductase activity is reduced by 50% in the presence of 2 mM UDP, 2 mM UDP-Glc or 3 mM UDP-GalNAc. Activity is unaffected by metal ions. kcat is 0.9 sec(-) with UDP-GalNAc. kcat is 0.99 sec(-1) with NAD(+). Homooctamer. Belongs to the Gfo/Idh/MocA family.