While Karlov Watchdog is on the battlefield, opponents can't attempt to turn face-down creatures face up either by paying a disguise or morph cost or by paying the mana cost of a cloaked or manifested creature.

It doesn't matter what happens to the creatures in response. As long as you attacked with at least three creatures, creatures you control will get +1/+1 until end of turn when Karlov Watchdog's triggered ability resolves.