Hmmm interesting, this is not something I have come across in my experience, and I have installed ESXi 5 hundreds of times on various hardware, Dell, HP IBM etc...If there is such requirement this would have been in the installation guide, but I doubt this is the case.
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vfk
Systems Manager / Technical Architect
VCP5-DCV, VCAP5-DCA, vExpert, ITILv3, CCNA, MCP