Interesting, could you possibly explain how "halt behavior" indicates that ECC is fully functioning? I've just read a lot about ECC being compatible but not tests explicitly showing it works.
Though perhaps the rare frequency of cosmic ray flips makes that acceptable.
When systems rebooted with less memory than the system configuration database said they should have most of the time there would be a multi-bit error detection, machine check, and 'memory update' in the IPMI buffer.