I haven't done much with radiation zones, but I know that if they're working they can definitely mess you up and/or kill you, so they do work.
Unfortunately I haven't seen any indicators to let you know if radiation zones are working.
The only way I know of in the "vanilla" Ravage is to have a Geiger counter on your character and active.
Other than that, I have looked into a mod that may be a good alternative;
JSHK Contamination Area Mod
https://steamcommunity.com/sharedfiles/filedetails/?id=944344838

I haven't used it in a scenario yet but seems like it may be worth looking into.