Nah, the CG isn't a DoT weapon at all. DoT means hitting once, then doing damage for a specific time after that. Imagine a poison arrow or something. The usual implementation in a game would be a projectile that deals a small amount of initial damage (as it hits) and DoT (the poison) thereafter. The difference between stacking and non-stacking DoT effects would be, well, if they add up or not. Back to the poison arrow example: It hits, the DoT effect starts, the target is poisoned, what happens if you hit another time? Do the DoT effects add up and deal double damage, is being poisoned twice worse than just once? If the answer is "yes" then you have stackable effects. Non-stacking DoT would mean you can only be poisoned once.
Maybe the second hit would increase the DoT duration, but that's it.
If you want a "continuous hit-scan wep" (I'm thinking of Q's Lightning Gun here), just increase the RoF (rate of fire) and decrease the damage, maybe increase the projectile speed for less leading (additionaly: get rid of overheating) . That way would require the least scripting effort I'd imagine, as you just have to change already existing values.
Edit: Ninja'd by Volt Cruelerz, but yeah, what he said.
