I don't know how widespread it is, but recently I've "busted" two stealthed groups because sorc pets weren't stealthed. All players in the group were invisible, but a clanfear and twilight were plain as day. In both cases it was 2 pets, so maybe it's a recent bug impacting having both pets toggled?
Battle not with monsters, lest ye become a monster, and if you gaze into the abyss, the abyss gazes also into you. ~Friedrich Nietzsche
At launch, no pets could sneak and you could use vanity pets in Cyrodiil, too.
Then they said they'd make pets go in stealth with the player and removed the vanity pets from Cyrodiil.
Well, the pets don't sneak though. Too bad.
DAGON - ALTADOON - CHIM - GHARTOK The Covenant is broken. The Enemy has won...
They're supposed to go into stealth when you do, but i suppose if they attacked something and are still in combat with it then they would probably be visible.
Well bottom line is my pets give away stealthed groups I love my pet build but cannot play it because my pets vs entire groups position....easy decision...