The short answer to your question is no. To our knowledge there's never been a topless eatery in Las Vegas, not least because Health Department regulations require food servers to maintain certain standards of personal hygiene, which semi-nakedness does not really comply with. Many gentlemen's clubs serve food, with some, including Treasures, Rick's Cabaret, and Badda Bing!, boasting pretty decent kitchens; while there will obviously be topless entertainers on the premises, the food servers are clothed, albeit often skimpily so.
The closest that Las Vegas has come to a topless restaurant was Sexxpresso, a drive-through coffee stand located at 670 E. Flamingo, where the "bodacious baristas" (servers) wore lingerie at work and were encouraged to flirt with the customers. It opened in 2007 but lasted only for a year or so. A Little Off the Top hair salon, which also sported lingerie-clad staff, eventually closed due to complaints (it reopened as Curl Up N Dye on W. Sahara, but the staff are now fully clothed).
There have been experiments elsewhere in the country, with topless donut shops being a particular favorite. Fort Collins, Colorado was once home to Debbie Duz Donuts, while for many years Ft. Lauderdale, Florida was home to R Donuts topless joint. Maine has been home to at least two topless eateries that we know of, but Mark's Topless Donuts closed in February, 2009 and the Grand View Topless Coffee Shop, which opened the same month, was burned down in an arson attack in June of that year.
