Wheel hats worn on the ramp are a FOD hazard. Unless they are secure on the head, which a wheel hat isn't, they should be left in the cockpit. Which is cheaper, an engine replacement from a hat being sucked through it or to have your head exposed to the elements for 5 minutes? I have watched a couple of hats get sucked through engines over the years so I know it is a real hazard even if it isn't very frequent.
It's not the completeness of your uniform that keeps you out of trouble on the ramp but the visibility of the airport's SIDA badge or your company's employee badge on your outer garments that does.
