I've been using an ability that uses this:
numEntityModifiers 1
entityModifier
buffEntityModifierType "ChanceToHitAsDamageDealer"
value
Level:0 -99.000000
Level:1 -99.000000
Level:2 -99.000000
It makes the ship that casts the ability impossible to hit, the ability only works for a short amount of time. I suppose this simulates stealth because enemy ships can't lock their weapons onto the ship.