I've heard this from several sources, but is it worse than any other FS? I mean it seems obvious that data corrupted in RAM will be corrupted when you write it to disk. I think people are worried about software RAID vs hardware RAID, since all hardware RAID platforms have ECC cache and software RAID should too.
It is worse as ram corruption can cause a loss of the entire zfs pool. there are no zfs recovery tools available, so data recovery can be next to impossible or very expensive.