corvettes aren't exempt. the cop could write the corvette guy a ticket anytime he wanted.
look at that pic. see the little rectangle in the middle of the front bumper? that is removed by two screws on the bottom of the bumper and it then houses a place to mount a front tag. thats where the corvette is made to have a front tag. just that most owners don't put them there doesn't mean they don't exist.
http://www.corvettemuseum.com/specs/2004/images.shtml
now as for the c6 I believe it just bolts onto the bumper with the bottom of the tag hanging down.
KEvin