I think Sal has stated in the past that the patent covers round holes, but Spyderco may also have patents on other shapes.
Gerber has used a jellybean shaped hole, I think without license from Spyderco. Benchmade used a round hole in the AFCK, licensed from Spyderco. My theory on why they've switched to the oval hole is that the license ran out and Spyderco isn't renewing licenses to competing manufacturers. If that's true, then the oval hole isn't on license from Spyderco.
I've tried all these holes, none of them work as well as a round hole so far. equipped.com points out that the oval hole makes sense, since the tip of your thumb is oval, not round. But what happens when you open the blade? The blade rotates, so the hole rotates, but your thumb doesn't want to rotate at the same pace, so the oval doesn't work as well.
Joe