I wonder what they're thinking. At least with nVidia there's a plausible sounding defense that goes like "hey, we just wrote a shim to load this platform independent code we already had lying around, so our platform independent code can stay proprietary because it's not a derived work of Linux". I don't think this position is correct, but I can see that it at least requires a court case to adjudicate.
But in VMWare's case, it appears that they took the Linux kernel and modified it to make their own vmkernel. I can't see how you make an argument (that their vmkernel is not a derived work of Linux) that takes more than ten seconds to soundly defeat.