We don't know if he did or he didn't, they only make it known against the Vong. And Wesker, emerald lightning is defined as an instakill technique, so what does that tell you? Sure a blaster to the head is an instant kill, but Traya's technique is called an instakill, and so is Luke's. They wouldn't have called it that if he couldn't use it on force users.
Well he is right, the technique has never been used against a force user, so we can't just assume it would work against a force user, or kill a force user unless we some logical reason to assume as much.
Lightning for instance can instantly kill a lot of people, but force users can withstand it, at least some of them can.
Instally kills it opponent how was that said? Like it "always instantly kills it opponent" or Luke shot lightning that instantly killed its opponent?"
Anyways it depending on the force mastery is exactly the point, it wouldn't do well against everybody, against a lot of it wouldn't even have any use... Perhaps thats the same with Luke's lightning, and other insta kill techniques. I'm just guessing here though, I don't know but unless you know we can't just assume his technique will kill on impact.
What is with you people and instakills? So you're all saying that Kun, Traya and Luke can instakill Ragnos *rolls eyes*, why would their be no defence, most of the instakills (exception being Emerald lightning) originated from the Ancient Sith, so why would they have no defense, if they did, then wouldn't Ragnos be instakilling in between 150 years of ruling?
Also Emerald Lightning was not used upon a force user and like others have said, it does not mean it has no defense, just like DE Sidious;s own brand on destructive force storm, can be blocked as can Luke's emerald lightning.