A few thoughts:
#1 He should have shined his shoes. This is a given. I can't defend that.
#2 The "snide remark" may have been his attempt at humor when called out on his appearance.
#3 If a mission teaches you anything its that you can make a suit last. Thats fine in Guatamala, but in a business where money talks its not acceptable. He should never disagree with the man interviewing him about his appearance.
#4 Yes, Mormons are proud of their missionary service. It does make them different and they do wear it as a badge of honor. I like to think he was proud of what he did for the right reason. Lets give him the benefit of the doubt here.
#5 Mormons will always list family and religion at the top of a list of priorities. Its like Bronco saying football is 5th. You can hate him for that but its how they are. I wouldn't hold that against him. It doesn't mean he'd be a lousy employee, and it doesn't mean Bronco is a lousy coach.
Finally, this kid isn't ready to work for a guy like you. You're looking for a polished professional. This kid isn't there yet. I bet he'd be a great employee, but if he's not what you're looking for, what can you do?