The only thing that's important with a granite countertop, is that you are fastening the faucet either to the granite, or the stainless sink.
If the granite is laid over plywood, then you will need to cut out the wood from below the granite. That is most easily done by drilling a 1/4" hole from the top, and then going underneath and using that hole as a pilot for your hole saw. Eye protection and a lot of grumbling will help.
A faucet can not be tightened onto wood; it compresses and it will be a constant chore re-snugging it.
If the faucet is installed on granite, you may not need the plastic triangle for added stiffness. On Stainless, you will want it for sure. If you have room for the triangle on the granite, use it. The more the better.