Vietnam Glory Obscured is a total conversion for Command and Conquer Generals: Zero Hour that simulates jungle warfare during the Vietnam War with unique gameplay elements such as village occupation and reputation, jungle combat and modular construction.
In Game Screen Shot
Will there be any SA-7 for the NVAs ?
Yes.
Is the SA-7 upgrade on a unit-by-unit basis or is it a global upgrade?
The SA-7 (9K32 “Strela-2”) soldier is a actual separate unit there is no upgrade required for them.
In the very same way you would purchase or "train" a missile defender, Tank Hunter or RPG Trooper in Zero Hour you will do the same for the SA-7.
Correct, it is just an specific infantry you choose to build (train). They are available right from the start if you build the structure they come from.