Their target market is essentially private cloud space combined with turnkey rack space - a pretty common on-premise setup where you order not individual servers, but complete racks that are supposed to be "plug and play" in your DC (in practice YMMV, spent a month fighting combination of manglement and Rackable mess).
You can think in this case of the final product as pretty big hypervisor cluster that is delivered complete. I'll admit more than once I'd kill for that kind of product, and I suspect that the price/performance ratio might be actually pretty good.
The operating system in this case is used for internal service processor bits (compare: Minix 3 on Intel ME, whatever was that proprietary RTOS on AMD's PSP, etc. etc) that help keep the whole thing running and ship shape.