This is very much workload-specific. If you cycle your processes out of memory even once a day, the chances of seeing a random gamma ray burst is vanishingly small. Of course, I wouldn't host ZFS or a data store.
I've had systems limp along reliably while throwing EDAC messages every few hours. With non-ECC memory, they would have crashed and burned.
Of course, if you're seeing EDAC messages, you'd be better advised to just shut down the metal and shift your workload to a different machine until you can replace the DIMMs in question.
https://en.wikipedia.org/wiki/Cosmic_ray#Effect_on_electroni...