Without the hash, we could detect a winning pattern mid-scratch and swap the result before reveal. With the hash, the result is locked. It closes that attack surface.
you are missing the point completely. the problem is not you changing the result mid scratch, it's that you know and can control the result before the scratch, because the seeds are generated by you.
and since you know which tickets are winners and which are losers, you can pick which ones to give to players.
not saying you are doing that, but you also can't prove you are not. so with how your system works right now, no one who knows anything about fair gambling is gonna play your scratch tickets.