The metabilsufite would add to the sulfite concentration in the developer. In B&W developers, it primarily acts as a silver solvent and in the concentrations as would result from campden tablets added to a lot of water, it likely wouldn't be objectionable. It might be a slight issue with lith printing, where controlled and small amounts of sulfite are used.
In color developers, sulfite has a very strong effect on the route through which oxidized developer links with the colour couplers, which it inhibits. Hence, addition of sulfite will reduce color saturation and also density. The sulfite levels in color developers are tightly controlled and rather small, and treating water used to mix/dilute these developers with campden tablets is highly likely to result in moderate to severe problems with color balance, saturation and contrast, particularly in negatives.
