^^ Do you mean how would the city of Las Vegas have developed if American was Communist?
Or, are we to assume that Las Vegas does develop as a gambling, entertainment mecca, and how is this characteristic influenced by US Communism?
If it's the latter, I'm not overly familiar with the status of gambling in "classic era" Communist regimes. My guess would be that, if it were allowed, and Vegas was the place for it, it would be tightly sequestered from the rest of the nation, and basically just used to bring in foreign currency and maybe entertain the domestic elites.
But all that would probably work better with a coastal city, at least pre-consumer airlines. Gamblers would just sail in, blow their cash, get laid, watch a show(probably foreign entertainers not afraid of blacklists), and then sail out. I doubt the authorities would want large numbers of foreign gamblers traveling inland by car or rail to get to debaucheryville.