noah - I would think that whatever it is (if on the coin) has already been accounted for in the grade. Maybe the coin was a 64/65 but because of that spot, ICCS gave it a 63.
As for value, this really depends on how you consider value. Are you buying the coin or the holder? I'm sure there's someone out there who would buy this based on its holder, in which case, no it doesn't decrease the value. If you're buying the coin, then yes it should have an impact on the value (given the choice between the same coin with or without the print, you would go without), but as I said, it could already be accounted for in the grade.
Keep in mind though, we don't know if it's on the coin, and we don't know if it's a print. He has a 14 day return policy, so you could buy it just to check it out (it would cost you shipping, but could be worth it).
Alternatively, you could look at
http://www.ebay.com/itm/120967746795I bought something from the seller last night. His ads are boring, but from what I've seen, the coins are top notch. I think you could get a good price on it.