I have made a cut out fondant jolly roger on a black fondant circle that I am going to put at the top of a buttercream frosted cake. The image looks a little "chalky" or dusty and I think that I saw the guy from "Cake Boss" misting fondant with water to make it go a little shiny. I think the image would look nice a little shinier. Should I do this? What are the drawbacks?
Yes, steaming with hot water will definitely make your fondant shiney and glossy. You might try rubbing with a little shortening, though, depending on the piece. If it's delicate and/or small, that might not work. But you have to be careful with steam as it only takes a few seconds to make the piece shiney. Too much steam will obviously melt your fondant. HTH!
You can also rub it lightly with a paper towel moistened with vodka or a flavoring extract with a high percentage of alcohol. The alcohol evaporates more quickly than water.
I have seen people on youtube boiling a pot of water, then holding fondant or gumpaste flowers over the steam for a couple of seconds to make them shiny. That seems easy, but I haven't tried it yet.