There really isn't enough aural evidence to deduce that it is definitely Benny Goodman on bass clarinet. As for historical evidence, well I haven't seen anything substantive, but then again I haven't spent a great deal of time looking! However, this morning I emailed Warren Hicks, the co-author (with D Russell Connor) of the bio-discography "B.G. On The Record", and wasn't entirely surprised when he stated "When I went on board with Russ Connor in the late 50s it was somehow just a given that BG was on that session. I don't know the origin of its being ascribed to him."
Once again, I'm not stating that it definitely isn't Goodman on bass clarinet, but I would like to know the original source for this (e.g. perhaps an interview in which Goodman named himself as the musician, or in which Norvo named him). At the moment, I don't know if the attribution is based on an assumption or a known fact, though the other sidemen listed as being on the recording - Dick McDonough and Artie Bernstein - obviously suggests a Goodman connection.
In "Lost Chords", author Richard Sudhalter devotes an entire chapter to Red Novro and his wife Mildred Bailey. The circumstances surrounding the In A Mist and Dance Of The Octopus session are discussed at some length, but give no clues concerning Goodman (incidentally, the story about Jack Kapp ripping up Norvo's contract sounds exaggerated if not entirely apocryphal). The most interesting quote is from Gunther Schuller, who describes the "Dance Of The Octopus" as "…..clearly the most advanced composition of the early thirties, falling almost outside the realm of jazz, and being in no-sense a dance or 'entertainment' music". Given the highly commercial constrictions of the likes of Brunswick at the time, it would be fairer, I think, to state that the record falls outside the realms of the recording industry and its narrowly-defined genres!