I see many topics argue about this, but none with an official rule or statement.

Stealth attachment from Imperial Black Ops stacks with the Hidden condition?

So if a group with the Stealth attachment attacked by a melee rebel, in the Precision count of the dices must have an 1+ Precision with a -2 Malus?

What's the source of the confusion?

The -2 Accuracy from Hidden is applied to the accuracy results regardless of attack type. Normally melee attacks ignore accuracy, so they are not affected by Hidden. With Stealth the accuracy in the attack pool during step 6 of the attack needs to be 1 or higher, or the attack misses.

There are a few melee weapons that guarantee 3 - 2 = 1 accuracy though (e.g. Vibrosword, Electrostaff). Shadow Armor could apply another -2 accuracy in addition to Hidden and make it harder to achieve the 1 accuracy.