if any ships in a fleet engage in combat all ships of the fleet become engaged in combat thus yes your ships will decloak to participate since the rest of the fleet became engaged
also if a combat begins in a sector all ships in the sector enter combat whether cloaked or not
ex fr my exp: my cloaked scout went into combat because to rival computer empires (whom i had tar treaties with)decided to have a battle just as my scout was passing by the sector to get to the wormhole 1 sector over
edit darn beat to the type again
