I think his argument goes to normal recruits too, not just questionable ones. If I just scout his players during the offseason, they're not gonna change a whole lot when I play them later in the season.
It could be as easy as just a toggle on the roster or player page, or even in preferences, to indicate that you don't want your players scouted. It should at least give a warning to the NT coach when on the player page or when attempting to recruit, and you can debate whether it completely prevents the recruitment or just gives the warning. Completely preventing it could enable some malicious actions from other countries, and I would assume most respectable coaches won't proceed after been given that warning.