If the opposing player happens to play this combo, does it happen to reveal the minion automatically? If not, what can you do against this fiendish combo other than wasting all your AOE cards?
A minion that is in stealth and given Taunt by another card will not act as a taunt until it comes out of stealth.
In short, nothing happens. The taunt can be applied to the stealthed minion but it will not be a valid target for the enemy to attack so it will have no effect until the stealth is removed.