Symptoms:
No selection for Red Hat Enterprise Linux 8 or CentOS 8 is available in vSphere during the process of creating or editing a virtual machine. This affects VMs with a virtual hardware version below 14.

VMware vSphere ESXi 6.5
VMware vCenter Server 6.0.x
VMware vCenter Server 6.5.x

Virtual hardware version 14 introduced new selections for Red Hat Enterprise Linux 8 and CentOS 8. See Virtual machine hardware versions (1003746) to determine which VMware product releases support this virtual hardware version.

On VMware products that support virtual hardware version 14, you can choose Red Hat Enterprise Linux 8 and CentOS 8 as the guest operating system only in VMs where you select or upgrade the virtual hardware version to 14 or later.

In all other cases, select Red Hat Enterprise Linux 7 or CentOS 7 as the Guest OS instead.

• The VMware Compatibility Guide is the authority on supported configurations of third-party hardware and software, including Guest Operating Systems, certified with vSphere/ESXi releases.  In the VMware Compatibility Guide, you will find that support for Red Hat Enterprise Linux 8 or CentOS 8 was introduced with vSphere/ESXi 6.5.
• The best practice for configuration of a virtual machine is to use the Guest OS selection that best matches the operating system running in the virtual machine. However, an exact match may not be available for a specific operating system. Typically this is a result of cases where a new operating system was released after a particular vSphere release already became generally available. In such cases, the result of successful certification testing for new operating system releases is published in the VMware Compatibility Guide along with links to KB articles with any special guidance, including the use of an alternate guest operating selections where an exact match is not available.
• Regarding the support of virtual hardware versions by VMware products see Virtual machine hardware versions.