Doug,
Seems unlikely. I've never had a GFCI fail before, so I can't imagine two being bad, especially since they are two different brands.
That seems to be the only thing remaining, though I don't understand how it could trip the GFCI if the DPST switch cuts it out of the circuit completely?
I wired the two bathrooms in our house the exact same way and we've never had a problem with the fans tripping the GFCI's.
Anthony