I am not sure what do you mean. According to this document: VMware KB: Best practices for installing ESXi 5.0 , The chipset and I/O devices are supported by ESXi5. The NIC are 82546GB which is also supported by ESXi5. I suspects it may just be some BIOS settings that have to be tweaked. Unfortunately I can't find any related information. The other part confuses me is that how could no one at VMWare knows why a certified system in 4 is no longer working in 5. I can understand it may not have any value to keep some old systems as certified. Particularly in this case is all component of the motherboard are actually supported and mentioned in the "Best practices".
BTW, I am also waiting answers from Supermicro. I have 4 of such servers with 24 cores each. About 16 production servers and about 100 non-production servers. I guess I probably will migrate to Hyper-V since the installation works fine and it also support Windows 2012 and most Enterprise Linux OS. Well, maybe it is time for a change after 10 years' with a solo-VMWare shop.