Not according to the manufacturers of SS showers. They are good with the drywall.
When installing a traditional solid surface shower, you are correct that the shower floor is installed first. Then the drywall is hung so that it leaves a gap above the floor (which may be caulked before the shower wall is hung, I don’t think the pictograph instructions for mine made that entirely clear) and the shower walls are hung on the drywall hanging below that gap and in front of the shower floor’s flange. This gap ensures that if any water gets behind the caulk at the floor/wall joint, the water never reaches the drywall to be wicked up. In the shower, any horizontal seams are interlocked so that water does not enter. Corner joints are either caulked or are caulked and covered with corner molding that seals out the water. Both Swanstone and Transolid instructions say that water resistant drywall is fine. One style of Transolid wall is already drilled out for all fixtures and handrails and the 1/4” SS material is backed with an aluminum mesh to make sheets rigid and that is glued directly onto studs. Ferrules are provided for all of the screw holes and studs must be placed according to the instructions.
European manufacturers of flatter shower floors , like Duravit, do not use a flange and instructions do not have them set into mortar. If I remember the one set of instructions that we were able to figure out, they even used the shower drain weep holes to take care of water that gets behind the walls and under the shower receptor. The joint at the wall/shower floor interface was just caulked, with no flange. I imagine these need waterproofing. I never understood the construction of these showers. They were not solid surface, I think, but more like acrylic. With manufacturers using pictograph instructions instead of words, even study of them can leave you perplexed.
Q