The big space shuttle used those for its maneuvering propulsion, and ground crews had to wear all the protective gear after landing until the propellant had been drained.
That brief exposure, before they got their oxygen masks on, put them in the hospital for a couple of weeks. It really could have been worse.
I believe the technical procedure for unprotected ground crew dealing with a leak of this stuff is, roughly, "turn around and run for your life." Hence the guys in funny-looking suits.
The emergency APU on F-16 fighters uses hydrazine and if it was used and the jet landed on a civilian airport (e.g. engine failure) then you need to have it safely washed before anyone can approach the plane. https://youtu.be/Puia_yQxir8?t=178