In which casino was this World Series of Poker discipline first offered?
2006 World Series of Poker:  Forty more events in various disciplines including Omaha, seven-card stud and razz, plus ladies' and senior tournaments led up to the 10,000 US$ no-limit Texas hold 'em main event starting July 28 and running through the final table on August 10. Omaha hold 'em:  The exact origin of the game is unknown, but casino executive Robert Turner first brought Omaha into a casino setting when he introduced the game to Bill Boyd, who offered it as a game at the Las Vegas Golden Nugget Casino (calling it "Nugget Hold'em").
Las Vegas Golden Nugget Casino