N.
I believe this is completely normal. Both my kids did this and niether of them ever sucked their thumbs. The drool can cause chafing or chapped cheeks and chin, but I don't really think there's much you can do about that. A very light application of Aquaphor or vaseline on his cheeks and chin might keep them from getting chafed, but I would just wipe my kids off when I could and let them enjoy their new-found chew toy. :-)