A viper room was also a common 20s New York City slang term for an after-hours club where hipsters would go to smoke marijuana and listen to jazz, typically located in Harlem. From the relatively ancient slang term viper for a marijuna smoker, from the hissing noise that one makes when inhaling deeply off of a joint.
The whole thing seems rather quaint and even cliche today, but at the time, it was all terribly cutting-edge. Jazz was a new music form, at least in New York, marijuana had only just become illegal, and nobody had really thought these things out yet.