You are a US citizen. He is an immediate relative of a US citizen. Consulate officers, by law, must assume that anyone (especially an immediate relative) who applies for a B2 visa has intent to immigrate illegally. The number one reason for visitor visa denials is lack of strong ties to home country. If his DS-160 can adequately show very strong ties to home, then maybe the CO will approve. I have my doubts, but he is free to apply.