Ghost does not have EMP ability any more at the current development stage.

For your information above questions,

1. Immortal's hardened shield is passive and there is no additional upgrade to get it.
2. Ghost's EMP took out Immortal's shield.
3. Once Immortal's shield was taken out by EMP, Immortal took full damage from Siege Tanks, which means there's no more hardened shileld.

I agree with that EMP is an interesting ability as well.
Right now, EMP is taken out from the game but as you know, this is not the final.
I will update you all when EMP's back to the game.

Isn't it in? I saw HDStarcraft use it before.