Right, but would you ever run VMWare on a fleet of RPis as a cloud of some sort? I mean, I guess you could, but it seems like a rather strange combination.
A cluster of ESXi servers doing vSAN and HA/FT is just another technique for making a given application highly reliable. There might be "better" ways to do it, but I look at this and see a very straightforward way to turn half a dozen Raspberry Pis into five nines of uptime (or more) for an embedded device.
You can roll out an virtualisation solution on raspis to many many many devices, perfect for making it rock solid. The arm server market is still very small, you will not haavy many customers able to test it, and much less risking using an still unstable solution.