In the pulse-racing revival of the musical 'Chicago,' which opened last night at the Richard Rodgers Theater, all the world's a con game, and show business is the biggest scam of all. It makes a difference, though, when the hustle involves a cast of top-flight artists perfectly mated to their parts and some of the sexiest, most sophisticated dancing seen on Broadway in years. By the time the priceless Bebe Neuwirth, playing a hoofer turned murderer, greets the audience at the beginning of the second act with the salutation 'Hello, suckers!,' it's a label we're all too happy to accept. The America portrayed onstage may be a vision of hell, but the way it's being presented flies us right into musical heaven.