Thank you for your question today, I look forward to assisting you. I have nearly 20 years of legal experience in various disciplines, including JAG.
It's not a legally recognized form of harassment that would give your son any particular rights against the Staff Sergeant. The SSG can very well state that his instructions were to keep an eye on your son, due to the constant concern of suicide relating to PTSD victims.
At best, XXXXX XXXXX can make an IG complaint or seek an Article 138 Court of Inquiry, which is really just a directed question to a commander concerning the activity. Either action might get this SSG off his back or it might make matters worse.
Now, I can tell you that any "evidence" that the soldiers find to try and use against your son, if it came to a court martial
, would be tainted and inadmissible. As a JAG, I'd want to smack this SSG for engaging in this directive, not because it is illegal, but rather, because any evidence turned up would be "command directed" without probable cause, which would render the evdience useless for court martial.
So, it is very likely that this SSG's commander would want to know, just to give an order to cease and desist with this stupid "spying."