Most VS stores do have at least one guy working there, actually. In the one back home, we've got actually got two, myself and then a guy who joined us during the summer.
Basically my duties involve stocking, visual merchandising (setting up displays and the like), and, what is actually probably my biggest role because I'm one of the best in the store at it, selling beauty (perfumes, lotions, splashes, etc.) Ocassionally I fill in at cash register too when there's a shortage and a long line, and I've even managed to sell a few bras and diagnose a woman's bra problem successfully. That last one made me feel aces.
But the precise role of a guy in a store will generally depend on its size. From what I've given to understand from talking to girls who work at other stores, at larger locations, stocking and visual merchandising is pretty much *all* they do. Medium and smaller stores, they have a lot broader range of duties.