That's not what the marketing droids said at a couple of seminars I've been to.
I'll have to look at their site, but I'm pretty darn sure that under ESX, Linux runs on the metal, which drives the VMs.
My opinion is this is more Linux BS, it never seems to end.
One of the other engineers in my shop is ESX certified Im going off of what he has told me. That it uses linux for a console but the kernel of the ESX system is not Linux..