So, my current plan is to get a Leatherman tread, and then use it as a watchband for some Casio G-Shock

There are many G-Shock watches from $40 to $7400. You should be a little more specific.

G-Shock lugs are very atypical and you should not plan on being able to fit anything to one that is meant to be used for regular watches.

Even with adapters, I doubt it would work out well. You can get adapters that allow you to use a 24mm single piece strap (NATO or Zulu style), or 22mm two piece straps (and one piece straps), however, they are not small and change the watch substantially and fitting any sort of bracelet to them, even if possible, would be strange I think.

Just by looking at some pictures, it doesn't look like a lot of them use the same style of lug-and-springbar combo that would befit a tread.

They mostly do use springbars, but the lugs are very narrow (in many models) and the straps are usually quite specific to the G-Shock.

I just haven't seen any specific guide as to which models are compatible with the tread

What watches are compatible?