Nope, the differential expansion works for any surface. I might also note that the difference between a slumped sphere and paraboloid is measured in microns and that is a very small dimension! The difference between the front and back for a slumped piece of glass would be more dependant upon the grinding rather than the polishing and figuring. You could have the center thicker or thinner, depending upon the end result of grinding.
As to the particular glass, I'd still want to use pyrex for it's smaller deformation with temp anyway.