No, that's a law for any non voters including poll workers. So if the candidate was in the act of voting it would be fine for him to be wearing his own button, but not if he for instance was just coming in to check on his election watchers, and of course if he was trying to talk to other voters. Basically no politicking within 50ft but the voter can bring in any handouts and read it in line and wear whatever they want as long as they are there to vote.

Edit: thinking about it more I think you are right the candidate could be considered different in this case and should not be wearing their own button. Although they themselves are recognisable as the candidate with or without the button.