I have read somewhere that some dice sites publishing a different hash from the acctual hash to fool people into thinking that their service was provably fair.
I'm not sure that has ever happened. One site (dicebitco.in) was found to be skipping rolls - if your next provably fair roll was destined to win then they would skip it and give you the next one. That's the closest to what you describe that I can remember. They shut down shortly that cheat was discovered. And of course it was only even discoverable *because* they were provably fair. That's what provable fairness does - it lets you detect when a site is cheating you.