The exact opposite, of "smells like ass". Unlike the previous phrase, "Vegas ass" describes hygenically and visually refined bottoms, or their associated scent. An ass one is more likely to lick, than find repulsive. Typicallly found on an exotic dancer, who works in a very high-end, Las Vegas "Gentleman's Club". Henceforth, the name.
"This place smells like ass. And NOT, freshly scrubbed, "Vegas ass" either!"