Are all polaroid backs the same

Example, I have a couple of Polaroid backs for a Bronica SQai, will that fit on something like a Polaroid 600SE or Mamiya universal?

No.

Backs are camera brand and model specific...a Polaroid Spectra will not fit a Polaroid 660E. The fact that it is 'Polaroid' film that it takes is that the film type ('instant film') is the only thing implied by that statement.