Guru, Id be hesitant to use the same brush for any combination of processes.
I do Gum Bichromate over pt/pd and use seperate brushes.
brushes may be somewhat pricey... maybe $30 or so a pop. may add up but when you take into account the (unlimited??) lifespan of the brushes, the amount of $$ in chems etc, buying a seperate brush for each process, even "nice" brushes, is well worth the investment.
only my two cents worth.