He could be craving red meat. Try a high quality mammal based dog food like beef, lamb, or venison.
Unfortunately scar tissue causes itching for dogs the same as it does people. Benadryl may be a better choice when he starts at it rather than the spray that he can still lick the residue. The other option is to apply the cone around his neck that they all hate so that he will not be able to chew at it when it acts up.
You also want to limit the time that the scar is exposed to direct sunlight as when the scar is exposed to too much sun it will cause it to itch.
Good Luck.