The abuse of the snake trap to grief people was what finally made Blizzard change their pvp flag mechanics, IIRC. You will not get flagged by using aoe near a flagged character in WoW. Now, I left shortly after Cataclysm so maybe they reverted that change too, but I was on a 90% Alliance server and I played Horde. There would have been endless opportunities for griefing if it were as simple as jumping into my aoe, and it never happened to anyone as far as I know.
I do remember flagged players jumping in and out of my aoe hoping that I would slip up and tab target them.
In TOR, my husband got flagged accidentally when he wandered into the wrong base. The NPCs ganked him before he could get out, and we laughed about it while we waited for his flag to fade... Then his healer companion put a HoT on me and flagged me too. /facepalm
Actually, now that I think about it, I believe Blizzard changed their pvp flag mechs before the snake trap, and that the snake trap was just bugged leading to "hilarious" fun. It was so long ago, I can't really remember - point being it does not work that way in WoW.