Have you tried vasoline? Maybe a little petroleum jelly would help soothe the spot. Don't put alot on just enough to treat. The dry hot heat could also be starting his paw to "Crack". Try to keep him walking on grass if it is too hot.
My dog Scooby chews on his foot alot too. It hasn't hurt him any. I had one dog that chewed on his toe-nails!!! I kept hearing a 'popping" noise and he was pulling at his nails! gross!
If there is any bleeding put some Septic powder on it. If you don't have that you can use Corn starch. Corn starch will work just as well for nail bleeding if you ever cut the nails too short!!!