Government job but medication due to disability?

My husband is a disabled veteran from the us navy. He has a 70 percent disability rating. He has torn rotator cuff and broken tendons and ligaments in the knees . He has been working since his release from the military with a company that contracts to the government.. After over 2 yrs of applying , gaining more work experience, He finally got the offer of a government job. These jobs are very hard to come by. He has been taking narcotic medication perscribed by his doctor and he takes very responsibly never has hindered his work ethic, no missed days, laziness, etc. Someone told him that he should rethink taking the job, because you arent allowed to take anything for pain when you are working a government job. My husband is determined enough that he would take the job and suffer in agony until retirement time, but does he have to?. does anyone know the answer to the question of whether or not he can continue on the same medication as he has for 3 yrs for a real chronic condition as a disabled vet.? They show disabled vet preferance so you would think there were loopholes. If anyone knows or has experienced this please respond