Hi Roz, you and your son are in our prayers.
Since he has been out of the service for a couple of years I believe you dont have too much to worry about. Unless his back problems stem from his time in the service, he should be ok to see any doctors of his choice.
Most RSD that began in the wars was from bullet wounds and such, and since he didnt get hurt in that way he is clear of any RSD from his tour of duty. That doesnt mean he couldnt develop RSD from a surgery, but we will be praying that doesnt happen.
Love you much, and will be praying