Sure, the corruption can occur, but if the memory is not faulty, ZFS will detect data corruption in-situ during a scrub. It's just that ECC errors can introduce their own corruption that is separate, during write operations only.
I believe if you have no choice but to use non-ECC (e.g. existing hardware that is limited by Intel's stupid design choice of "ECC is only for servers"), ZFS is still much better than using ext4. It still protects against a different class of errors which is HDD degradation. When used in RAID-Z it can even recover for them.
For perfect protection ECC is necessary. But this is not always possible financially. I think it's a bit of a wild statement to say that if you can't afford a server with ECC you should forget about ZFS entirely.