Senator McCain is well positioned to garner a significant part of the Hispanic vote. He has spent his entire career connecting with the Hispanic community in Arizona. According to Ruben Navarette he is well respected. He got 70% of their vote in his last election.
He also benefits from being on the sane side of immigration arguments. He has never endorsed the Republican party's stupid and suicidal positions on immigration. Clearly he knows the Hispanics for what they are; an honest, hard-working, family oriented culture.
Additionally, there is an antipathy by Hispanics to blacks. The Republicans managed to nominate the one candidate that moderate Hispanics don't mind fleeing the Democratic nominee to vote for.