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In pvp you are invisible to enemy players in sneak mode until the enemy faction crosses the threshold when they get too close to your character, so yes you are invisible in pvp while in stealth. I hope this help you.
Also, when you are first noticed by enemies in pvp you will become visible, but not fully. At the threshold of detection range they will see you as a hazy outline of yourself,, then once you are fully detected you become completely visible and your stealth will break.