Well, if you already have the
basics of the dark swarm system down, there's a few ways you could implement armor. One way (that I recommend because it cuts down some trigger work) is to handle "armor" by random probability of a shot causing damage or not. You can assign player owners to represent different armor types, then use your prefered VHP system for each unit. Higher up the player is, the less chance a shot inflicts damage.
The other way is to use combination of players and VHP. A 5 armor unit could by, say, P5, and it would have to go all the way down to P1 before it can start taking hits (from its seperate VHP, I mean).
To do it without player-based VHP, though, you'd need to either add the armor amount to the unit's VHP, or use a seperate VHP counter for that unit to store its armor value.
Depends on what you're trying to do, though. I recommend the random probability method, personally.