I know you never see Vivi without his hat, but it'd be interesting to see like when he's going through Dali, or when you catch a glimpse of the Black Mages being manufactured or thm marching out at Kuja's orders, maybe that would be your best chane, but I wouldn't bet on it.

I'm guessing his head though would just be a rounded out black ball. Thos eeyellow eyes though...now those are killer look'n eyes. Definitely awesome.

no its a mystery

They never show Vivi with out his hat but he might not be bald, he might have long, flowing blonde hair