Question: Why was Bloody Mary's singing voice dubbed, given that Juanita Hall was a strong singer who had performed the role on Broadway?
Answer: Richard Rodgers was just being Richard Rodgers. He allowed her to sing in 'Flower drum Song' on stage the following year, 1958/9, and allowed her to use her own voice in the film of 'Flower Drum Song' in 1961. He had his own demons then and was just reacting.
Question: I have heard that the role of Bloody Mary was dubbed in this movie. Who dubbed her, and why isn't that person listed in the credits (given that Giorgio Tozzi, who dubbed Emile de Becque, is credited)? Also, were Nellie and Lt. Cable dubbed? Again, no one is credited, but their singing voices sound dubbed to me. Can anyone shed some light on this?
Answer: See http://www.imdb.com/title/tt0052225/fullcredits#cast. Bloody Mary's singing voice is Muriel Smith, Lt. Cable's is Bill Lee. Mitzi Gaynor (Nellie) does her own singing. For most of these "on-location" musicals, the singing is recorded in a studio, so even the actors who do their own singing are, in effect, dubbed by themselves.
Question: Why was the "I'm Gonna Wash That Man" number severely hacked about for the film and is not the same as in the soundtrack recording?
Answer: Richard Rogers preferred the vocal performance of Muriel Smith who played the part in London. Since the vocal tracks for musicals was recorded separately from the filming back then, dubbing occurred for many reasons other than lack of singing ability of an actor, scheduling problems, budget, etc.
Myridon