I have a 25 and love it! I use a full size Sarah wallet or a full size red leather Coach wallet usually and have not had any problems.
As long as you don't get into a rush to take your wallet out or put it in it should be fine. You could scratch a wallet on any bag with a zipper if you were in a hurry I think.
My Emilie wallet has been scratched so many times by the zipper, not just in the 25 though, all the other bags as well, because i tend to be in a rush to get my wallet in and out of the bag. So far, the canvas is still in perfect condition I guess it's true what they say, LV canvas is indestructible