I've ran one or two tournaments and thankfully haven't had to turn anyone away for having a non-gw models in their army. I operate the same rule as my local store does, 75% of your model has to be GW and that's the same with the army. I tend to be more lenient towards IG and Orks as there are many different patterns but as long as
On a personal level, in pick-up games and the like as long as they look better than the GW model that's ok and are absolutely like the models they're representing. Things like the avatar of war miniatures and other high quality models are good with me.
Welshman