The "stock" hands technically belong to Cyborg Arts. So, you would likely need to license from him to use in a commercial pack.
Simon's hands can be used commercially but only for FPSC which means they would be incompatible with the model pack license which allows for use in any engine.
Your best bet would be creating your own rig and hands to use because then you won't be beholden to another artist and you can build your own product line. Being able to tailor things to your aesthetic tastes should be an added bonus.
It may be an intimidating task to take on but it's achievable. When I made hands for MP9/10 it was my first attempt and so far from perfect but they're still kicking around all these years later.
edit: I know bond1 and jfletcher have both released FPS hands on this board but I don't know the licensing for them.
Best of luck
