I agree with @tim5055, you need to take what pool builders say with a grain of salt (haha, pun definitely intended!!). No steel structure buried in the ground is going to be corrosion free and the significant degree of corrosion you described is more likely the fault of the original PB uses a substandard grade of steel and improper bonding than the fault of the salt water chlorine cell. See
THIS ARTCLE for a good primer on how stainless steels corrode in soils and concrete. There are also grades of steel that are DESIGNED to corrode a bit so that they form passive oxide layer that then becomes a barrier to further degradation. In those cases, using an angle-grinder to remove all of the "rust" and then re-coating it with Bond-O is exactly the WRONG thing to do.
To the OP - there is an article in PoolSchool on proper bonding and grounding and the differences between them. As long as your PB is ensuring that all of your equipment is properly bonded and appropriately grounded, then the increased salt levels will not cause you issue. The bigger problem is that many PB's don't understand the Do's and Don'ts of material compatibility with salt water (like not using cheap aluminum fasteners with salt water).