They did publish the source to the GPL drivers as well as to the vmklinux “adapter”, and I don’t believe either the core hypervisor or the ESX kernel were derived from or adapted from the Linux kernel.
My impression is mostly people are annoyed that VMware drafted off the Linux driver ecosystem and used it to help bootstrap a proprietary ecosystem.
Eventually (once they were successful) they published a native driver SDK and hardware vendors wrote native drivers for it.
To me this seems very similar to the way Linux had for a while a way to run Wifi drivers originally written for NT, though it didn’t lead to the year of the Linux desktop as some of us might have hoped for at the time.
