Do you prefer that Vehicles have no crew? That way your pawns would become their crew ( The Recio you hired would be shooting the weapon, your Leader would be in the front ordering the crew what to do... ). Although in that case open Vehicles ( as charriots ) wouldn't have miniatures sculpted on it, or would be ones which wouldn't be the real crew of it.
Or do you prefer each Vehicle would have its own crew and the pawns of your bands could only be its passengers? Although in that case Vehicles would be more expensive in Maravedies and you'd have to hire less pawns for your band.