The Merchant Of Venice isn't even racist... There is nothing against being Jewish in there. In fact, if anything Shakespeare is commenting on the corruption in society. The fact that Shylock happens to be Jewish is just a means for setting up the plot since there were only Jewish money lenders in Venice.
The authors voice may make it into pieces of literature, but unless he is deliberately referring to himself (which Faulkner isn't, seeing as he writes fiction) there is really no point looking for it, other than to unveil more aspects of the content. As StLukes said on another thread, which character is Shakespeare in his plays? No one knows, and it doesn't matter.