To the OP, yes they can. but mostly at higher speeds. Cleaning up/smoothing out the undercarrage is a big deal, most new cars have plastic panels to accomplish this. Rear wings usually work at higher speeds, but testing and road time are important. Most of the ones off the shelf are a waste of time and money.
Here are a couple of interesting links
one
two Check out the archives at that site-too many links to add.