I wonder, why would you want that ?
PlasmaC already has a torch disable button on the screen so it will do everything except switching on the torch, then when you are sure everything is fine you enable the torch and the machine does it's thing.
On topic, yes that will work.
I just like to have an extra layer of safety to protect against a software failure or board failure. I realize this is unlikely but it makes me feel better so I do it. . I have one on my other plasma controller that is connected in series to a mechanical relay. I know the outputs on the 7i96 need protection from switching inductive loads. I don't see any issue adding the switch to this but was being cautious