The Oracle VM Server for SPARC software depends on particular Oracle Solaris OS versions, required software patches, and particular versions of system firmware. For more information, see Fully Qualified Oracle Solaris OS Versions in Oracle VM Server for SPARC 3.5 Installation Guide.
The version of the Oracle Solaris OS that runs on a guest domain is independent of the Oracle Solaris OS version that runs on the primary domain. So, if you run the Oracle Solaris 11 OS in the primary domain, you can still run the Oracle Solaris 10 OS in a guest domain.