Could you see just the 'ball' or the player as well.
Cause it SHOULD allow you to see hidden players, and if the other players are using it, it also SHOULD allow them to see you.
Normal detection of hidden players is 10 meters (less with some skills and armor), with the skill active, you can detect hidden enemies at a range of 20 (less with some skills and armor)
So if NONE of them were using it, but you where, you should be able to see them and they not see you (if your hidden)
But a single player on their side using it, they ALL will be able to see you (at 20 meters)
This is why all raid groups in pvp have as least one player using this skill
The bright ball means nothing, (like having pets out). If your in sneak, it does not matter, you, the bright ball and any pet, they are all invis.