Weird. Personally I wouldn't do it. I can't think of a single reason that you might want to dilute your rennet with salt water (and that's a lot of salt!). It's a weird recipe anyway. The defining characteristic of a Jack cheese is that you wash the curds with cool water (like a traditional Colby), so this is pretty weird.
Well, let me rephrase that.... I'd be tempted to try this recipe just to see how it worked :-) However, I would not take this as an example of a classical Jack recipe.