Perhaps some of the more chemically inclined can chime in here. The stain might be more or less vulnerable to sulfite after development depending on the type of developing agent, or perhaps after development a fair amount of sulfite (for example the amount in TF3) can be tolerated. But I've always read that a fixer like plain hypo (ie no preservative) is ideal for stained negatives, and that you definitely don't want to use a hypo clear at the washing stage since since a hypo clearing agent is basically all sodium sulfite with some bisulfite added to bring down the pH.