Ok, so even if the ESX 4.1 host servers are in the vCenter 5.1 as stand alone servers (not in a cluster) the VMs still retain the original EVC features from the previous vCenter 4.1 since those hosts are in an EVC cluster there...is that why this is the case?
If that's so, then I would need to make sure that either the new ESXi 5.1 EVC cluster is using the same Intel Xeon chipset family or do cold migrations...got it.