I think it's pretty clear Luke did use Force Choke--to disable, not to kill. Could he have rendered the guards unconscious in another fashion? Probably, but in its own way, this was one of the less violent methods. The thing is, most techniques within the Force are dependent upon the user's mindset as to whether they're Light or Dark. If Luke had no malice or intent to kill, even if he used Force Choke, it's not Dark Side. Remember that he eventually learned to use Force Lightning (as had Plo Koon before him) as a Light Side technique.
THIS, and I'm surprised most people don't get this.
It the technique Force Choke? Yes. Was he trying to kill anyone with it? Likely not. I could take a shock probe and use it to kill you with a sustained charge into the heart, or I could just use it for a second to incapacitate you and keep you down. Just because the technique can kill doesn't mean it can do ONLY that.
The Gammoreans could be dead, or they could have passed out. If I apply the sleeper hold on you you will be deprived of oxygen, be "choking" as it were, and eventually fall unconscious. I.e. you will go limp and fall down. That doesn't mean you're dead.