As per the below VMware HCL page, OEL-5 is fully supported until ESXi 5.1 U3. Post 5.1 U3, the support will be in legacy mode.
The Legacy support level is between Supported and Deprecated. These guest operating systems are typically no longer supported by the original vendor. As a result, VMware's ability to support this guest operating system is reduced because VMware may not be able to collaborate with the OS vendor to provide the highest level of support.
VMware Compatibility Guide - Guest/Host Search
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Cheers,
Supreet