When initially exploring ESXi I ran it off a USB thumb drive. I installed it as a pass-through drive to Workstation on a desktop and did all the initial work before unplugging the USB and popping into a server. Worked fine.
I suspect that the reverse is entirely possible, physically clone the install drive and setup an empty workstation vm with the cloned drive as a physical pass through and it should boot up. You need to ensure you enable virtualisation bits to pass through, but that's about it.
If I remember right using Converter against a physical ESXi is banned by the Geneva convention.
It is considered to be inhuman and more important completely unnecessary.
To convert a bootable USB-stick to a Workstation VM you either directly boot the VM with the same stick - or use dd to copy the stick to a monolithicFlat Workstation VMDK (one piece preallocated)
But to tell you the real important aspect : this idea of you makes zero sense.
The disks the real ESXi saw as real hardware will not be present in the virtual VM.
Same with the nics - this means all the configuration details you want to look at will be invalid anyway.
So the whole plan is a nice training experience - but you will not be able to use the virtual ESXi for any validation.
Even if you clone the whole machine including all datastores and so on - the behaviour of the ESXi VM will differ so much from the original that it makes no sense to even try.
What we need to do is to evaluate a customers ESXi Server for a contract mgr.
It does not have to be a fully functional ESXi Server, although that would be nice, but we would like to view the networking setup as well as other ESXi configuration information.
If not converting their ESXi Server, is it possible to create a nested setup where we install ESXi 6.7 on a VM and import their configuration info?