Yes.
Ben Siegel came to the West Coast in 1933 to muscle in on Jack Dragna's LA rackets. He visited Nevada many times. In 1941, he was charged in the murder of a NY mobster who was trying to hide out in California. A jury acquitted Siegel, but he though it best to lie low in Vegas for a while.

Vegas had been a boom town since 1931, when gambling was legalized statewide. Siegel found seven hotel/casinos there, including several that were air conditioned, all of them built int he Western "ranch corral" style. He tried unsuccessfully to buy into the El Rancho Vegas. He did succeed in buying the El Cortez with money from his NY mob partners (probably Meyer Lansky, Joe Adonis and Frank Costello). They sold less than a year later and nearly doubled their money.

Siegel next set his sights on a partially built hotel on the edge of today's Strip. It was already called the Flamingo by its owner, Billy Wilkerson, a degenerate gambler whose losses left him without money to finish the hotel. Siegel bought him out and convinced his Cortez partners to reinvest in the Flamingo, which opened on December 26, 1946 and lost money (as I said earlier). He was murdered on June 20, 1947. Within an hour of his death, two big-time, mob-connected gambling hotshots, Little Moe Sedway and Gus Greenbaum claimed the Flamingo and started to make big money.

Siegel didn't "invent" Las Vegas. His contribution was to build the first hotel/casino in the modern, Miami Beach-style that was very different from the Western corral style of the other hotels. The Flamingo set the pace for Las Vegas's growth with other modern style hotels in the Fifties because people from other parts of the US preferred it to the Western frontier theme. The guy who really built Vegas in that period was Moe Dalitz, a big-time Prohibition-era gangster from Cleveland.