Life support on underwater vessels has more to do about filtering out carbon dioxide rather than providing oxygen. In normal air with 21% of oxygen, carbon dioxide may be deadly in concentrations of around 10%. Just plugging another bottle of oxygen would not have helped trapped Rudy Wells unless there are means to filter out carbon dioxide from the vessel's air.
Parker's dialogue has been dubbed at least twice. Once when he says, "No backbone," and another when he says, "Now we wait, but not for long." It is obviously not Parker's voice.