How did he acquire this ticket? It sounds rather dodgy, but if he got it through a legitimate channel, such as one that required him to enter a government ID number or his government agency travel office, I wouldn't worry. If a military person bought it for him or if he purchased from a questionable travel agent, my reaction would be that if it's too good to be true, it probably is. Can he see the fare rules, which might be more explicit about about applicability and ID requirements.

If he is not entitled to use the ticket, the consequences could be denied boarding in either direction, possibly with the need to buy a walk-up fare, ex psot billing for a full fare ticket, closure of FF account and forfeiture of miles, and a report to his employer of fraud in the use of special military air fares to which he does not qualify, possibly leading to termination for cause or even civil/criminal fraud penalties. Is it worth the risk if he cannot verify that he is entitled to the fare? Has he tried to ask his agency about this?