Those concentric rings are found on copper washers used on brake systems. The rings touch down on the irregular surfaces that you speak of, Greg, and they actually crush a little bit. These washers, if you can find them, are excellent.

I have reused these washers on brake systems and have been successful when a brand new flat washer would not make the seal.

The RTV will probably work fine if all else fails. But, if the washer is the correct size and the pan is new, I don't see how it will leak if the bolt is torqued to anything past hand tight.