i work in a rehab facility and any kind of benzodiazepine (valium, clonopin, ativan, etc) is almost always given to people for withdrawing from alcohol, and it is major in keeping them from having a seizure. valium in itself is actually very low in addictive quality, unlike opiates, and since it is being given under the care of a doctor, the doctor will be able to taper him off of the valium to avoid him becoming addicted to its effects.
rest assured, im sure his doctor has years of medical training, is experienced in working with addicts/alcoholics and will be able to curb the possibility of him picking up valium as a drug of choice. and i'm sure you could talk to the doctor if you had any concerns. hope this helps! =)