I tried to make a lab environment similar to lab in CBT Video Training for vSphere 5.5 - three esxi hosts, domain controller and vcenter server would be virtual machines inside vmware workstation. Major difference would be me having virtual not physical host running windows 7/8.1 and workstation software on it. Whatsoever I did what you told me to do and ESXi 5.5 was successfully installed - so point here is that vm running esxi 5.5 as OS is treated in existing vSphere 5 infrastructure as any other vm thus it is a safe mechanism for learning and testing purposes. From now on I will install two remaining esxi hosts and follow lessons as they are in video course which is awesome.
NOTE: A few years ago I had physical esxi hosts for testing purposes but they are too old now, do not meet requirements for esxi 5.5 so now for the first time I will deploy esxi hosts as vms. I am pleasantly surprised to see this nesting works out of the box without any configuration changes.