Oracle VM Server for SPARC supports Solaris 10, and Solaris 11 for both guest and host operating systems.
At this time, there are no mainstream Linux distro's that offer support for Oracle VM server for SPARC, although in the recent past Ubuntu and Wind River have.
No Microsoft Windows support.
The modern SPARC platform ( sun4v ) is locked in Solaris. No chances for open-source OS'es like Linux or *BSD.
This is because the important hardware documentation is closed ( known only to Sun / Oracle engineers ). For example:
* virtualization features of CPU are documented only at hypervisor-call level (part of Sun servers' firmware), and only partially.
* CPU errata are closed ( Some errata for old UltraSPARC III were opened during OpenSolaris project, but that's all).
* crypto features ( SPU and MAU ) are closed.