This isnt really about how stealthy the weapon is.
You can place a trigger with detected by opfor with a single opfor unit in the entire map inside the trigger, shoot that opfor unit with silenced weapon and even if its one hit kill from a headshot the trigger will still fire. Weather theres no other enemy ai on the map or an enemy ai 200m away it does not matter, you will still be detected.
Right now there is no way to make stealth kill missions unless you use unnecessary scripting or plan on having the player go weaponless so that they do not fire a single shot toward an enemy.
If an enemy with no other enemy around is dead before they know you are there then you should not be detected.