vmnix aka Service Console aka Console OS aka the Fuzzy part, was part of ESX, which was discontinued with the 5.0 series of ESX products.
(Is the word "vmnix" wrong? Does it apply only to the entire Red Hat-ish distribution in the COS, and not to the Linux stepping stone alone?)
Basically the old 1.0 - 4.0 process for _ESX_ was like this:
* Bootloader
* Linux Kernel boot
* Load VMnix module.
* Load VMkernel
* hardware control passed to VMkernel
* Linux continues running as a sort of 'super' VM with some limited hardware access.
For _ESXi_ from 4.0 - now :
* Bootloader
* VMkernel
I don't know if this was to make the transition for stuff like vpxa from ESX 4 on easier internally, or to make it easier for 3rd parties to develop against, or both.
Is it lazily wrapping some functionality that should be open sourced that fills in where the service console would normally be? Probably not, but I can see why people would be a little suspicious.
vmnix was the name of the Linux kernel module that was loaded during the Service Console's boot process.
The terms "Service Console", "Console OS (COS)" were at times used interchangeably and referred to the Redhat distro you logged into at the terminal.
VSphere 4.0 had 2 versions: ESX (with COS) and ESXi (without COS). In 5.0 the COS was removed entirely.