If you're spinning the ball a lot, the contact patch won't be much in that missing part, so I wouldn't expect much change in play. It's when you hit closer to the center of the cue ball that I would expect slightly funny action.
The contact patch is typically a quarter inch across with the force largest near the center of the patch for a normal tip. I think the effective offset, which sets how much spin you are going to get, is a kind of weighted average over that area. If a half-moon is missing from the patch, the center is unlikely to be where you expect.
If you want to test for an effect, see if your stun draw works like you expect for intermediate distances below center.
