When playing as a warg, you can go into a rez circle by getting 1 shot stealth up and going behind where the flag is. Sprint towards the flag, and when you get close to the flag move just to the right a little bit so you barely miss the flag.

You will go in the rez circle. When you get in, move to the middle and don't move. If you stay still, when you 1 shot, they won't even see you.

Now you can rez kill freeps.