Stick and Shock are electrical, so they do stun.

I thought I read somewhere, but now I can't find it, that spirits (like vehicles and such) are immune to stun

Vehicles don't take stun damage. They are not, however immune to Stick'n'Shock. They just get affected differently in that there is a chance they are shutdown for a number of turns.

But that isn't because of their armour.

Stick'n'Shock works against Impact armour, which is the same rating as balistic with spirits. Instead of a value for AP, the Impact rating is just halved. Which does more than any short of AV rockets AP against higher armour targets.