I just scanned through the Altix 350 manual (which should be similar enough to the 330)
and it says that ECC memory is required. Interesting enough, it is rather unspecific when it
comes to memory. But it says "Only use SGI approved DIMMs", which, as I think, should
compensate for this...
Short: If I interpreted the manual the right way, non-ECC is a no go... but if you have some
non-ECC bars lying around it's worth a try maybe...