2bh it's not completely clear.
The Joestar mansion looks like a noble sort of aristocratic estate,
but George could have just been a rich English merchant.
I believe the implication is that they're nobility though, since Jonathan is just such a 'noble and too pure' sort of idealistic character.
But for OP, what >>2210
is best in my eye; Jojo is too goddamned fucking stupid for there to be any overarching themes of class,
even in a subliminal way.
I honestly doubt Araki could even comprehend the notion of economic class.
Dio is quite literally comically evil just for the sake of being so, and is not meant to be reflective of any particular type of human in general: Dio or DIO, he in particular is just an evil fucking bastard simply because he is
so don't bother questioning it.
And so is his dad.
SPEEDWAGON on the other hand is also a 'underclass dreg' sort of character, but he is the complete inverse of Dio.
He has honor and respect, he doesn't screw over everyone possible to get the upper hand.
He is a good person who also happens to be a leader of a mugging crew because he 'has to be' or whatever to provide for his family that was mentioned in one line.
So Araki is transcendently apolitical, but that doesn't mean he's actually injecting reactionary messaging I don't think; I'm fairly certain that he really just is that way.