Yes he will.
His supporters? Not so much.
But to be fair I don't think Obama's supporters would be as gracious as Obama in defeat either.
Actually, I don't think Obama is a particularly polarizing character. The only thing he really has against him is the fact is that he's half white half black - so plenty of whites will be sceptical towards him.
So I think if he wins, remember, it ain't over yet, most Republicans will probably be cool with it.
Political nutjobs can be found everywhere.
Fanatical Canadian schmoes, longing for a green card to be with their Cali Vampire Muscle Daddy can be found in both parties