It's not really about busybox. Conservancy started looking at the use of Busybox, and then realized that vmkernel was using the Linux kernel in ways that (in their eyes) violated the Linux kernel's license. The present lawsuit is about that, and Christoph Hellwig is suing as a Linux rightsholder.

Swapping out Linux in vmkernel would be much harder.

See their FAQ (or one of the other comment threads here) for more info: http://sfconservancy.org/linux-compliance/vmware-lawsuit-faq...