The funny thing is that Imdb calls the original release mono. As far as a surround channel being missing or not is unclear. There may have been one, but it certainly isn’t on the DVD. Compared to what most Disney Enhanced mixes sound like, the 3.0 is still preferable.

From DVDizzy.com:
The final soundtrack is one that purists would likely flock to - it’s a Dolby Digital 3.0 Surround intended to replicate the original theatrical presentation via faithful restoration. But in fully equipped theaters, Lady utilized a composite magnetic stereophonic sound process that would have boasted four discrete channels. This track only offers three distinct channels of sound - in the front right, left, and center speakers, with nothing at all emanating from the rear channels. That would seem to defeat the purpose of including this track at all, without the monaural rear channel that would have accompanied the CinemaScope exhibition (fueling the movie house’s side and rear speakers), this does not recreate the theatrical experience. One assumes that the mix employed for this has not been manipulated in ways that “Disney Enhanced Home Theater” entails, but I had trouble discerning much difference. In any event, if you don’t have a home theater and/or don’t care for remix jobs, this serves the viewer fine. But it would have made more sense to include a 4-channel stereo soundtrack or even the 5.1 remix that graced the Limited Issue disc. Nonetheless, I have a feeling that the majority of viewers will be content with the default 5.1 remix and may not know or care what Lady offered in 1955.