I haven't had any sort of problems with the dimple -free sticks at all, actually, so it wouldn't be a big concern to me. The sticks on the Logitech Wireless Action Controller I use now are pretty much flat but the rubber on there is pretty non-slick so no problems with slippage there.
Best wait a couple of weeks until we see what the actual controller will look like, which we should be able to see at E3. The one that had been shown around other confereences have only been mockups/prototypes and not the final design.