I talked to Sean and Richard about this, and have thought about this a bit. The consensus seems to be that it is fine to use bromide with an SWCG, but that you need to pay attention to what you are doing (like so many other things!).

1. Bromide / bromine does not damage SWCG plates.
2. Bromide DOES tend to increase LOAD on an SWCG because it de-stabilizes the halogen residual (which is, after all, the point of using it!)
3. Increased 'on-time', from whatever cause decreases SWCG life.
4. When using bromide, care must be taken to not overload the SWCG. This is more likely where the SWCG is switched by an ORP controller.
5. Bromide is primarily of benefit when CYA is very high (>100 ppm). If CYA is lower, simply adding bleach to raise the FC to an appropriate level would probably be a better choice.
6. When CYA is very high, adding bromide to achieve an free halogen residual may well be appropriate.
7. Uncertainties include the time it will take to convert bromide to bromate, and the appropriate bromide dose.