["Everybody's entitled to an opinion, regardless of whether it's informed or not."]
The SACEUR and Secretary General of NATO both hold "HEAD OF STATE" status, so as to be able to cut through red tape and contact anyone in the world in order to hold the Alliance together.
That, in my mind, puts General Clark above the level of "serviceman."
If he's wearing an American military uniform, regardless of what position he's holding, he reports to someone, and serves at their pleasure.
Your ignorance of our military chain of command is just a distraction, however, as you're avoiding the question of whether you consider any of the actions carried out by NATO during Operation Allied Force war crimes.