MMH, hydrazine, UDMH, Aerozine 50 will react with material with high iron concentrations, like stainless steel 440c (used in quad check valves), solenoid magnetic material. They also react with many types of plastics like pvc, kapton (solenoid insulation) to break them down. The most common type of soft good in valves is Teflon based and many components are stainless steel or titanium.
Aerozine 50 would permeate and damage our fully encapsulated suits at white sands test facility in under 30 minutes but MMH would have no affect.
In general the hydrazine family is fairly easy to deal with from a hardware side. Personnel exposure is the largest issue since they all cause cancer. If you have smelt it you have been over exposed. I know 5 or so people I have worked with at white sands test facility who have died of various types of cancer.
N2O4 is far harder to deal with as it reacts with far more material, builds up salts on surfaces, and when moisture is added forms nitric acid. It will cause burns on skin and eyes, and if it's inhaled it can cause severe damage or death.