My only experience with Pau Ferro (Monkey Pod) is helping saw it on a Wood Mizer. I have worked with Cocobolo with no reaction, however I have had reaction to Brazilian Cherry (Jatoba) it made me itch and turn red, no rash so to speak but definitely gave me a red color to my skin and itched like crazy.
my take on wearing disk masks is as follows... If the mask does not filter out 1 micron to .5 micron or finer, it really is not going to help protect you from the "dangerous Dust Particles". It is the fine dust that is dangerous. Now a mask may help keep you from sneezing, and from having snot the color of the wood your working with... a better solution is to plane, scrape and rasp as much as possible and sand as little as possible, and have good ventilation. The end result will be nicer also, at least in my experience.
At least thats my take.