Typically, yes. A vest (waistcoat) should properly cover the waistband of one's pants. Consequently, a belt will tend to protrude under the vest, adding girth, drawing the eye to the waist, and ruining the smooth line.
Freakish exceptions may exist, of course. Few rules on proper attire are utterly without their exceptions. But that's the rule, and the reasons behind the rule. And because it's a pretty well established rule, I'd advise against violating it even if your belt and buckle are so thin that they'd be invisible beneath the vest. Or even if you're wearing your vest over low-riding jeans, so the vest doesn't cover the waistband - which tends to be a horrible look, btw.
It only matters because of the thickness of the belt, so why not wear a D ring belt or the like? If the conditions for the rule having to exist are not met, feel free to ignore the rule.