If you configure the server with Oracle VM Server for SPARC, you can install various combinations of the minimum (or later) versions of the OS. For example, you can use Oracle Solaris 18.104.22.168 for the control domain, and Oracle Solaris 10 9/10 in guest domains.
Note - Oracle Solaris 11 is the recommended OS for T4 servers. The advantages of Oracle Solaris 11 include simplified installation and maintenance, enhanced virtualization capabilities and performance enhancements. A more detailed list may be found at: http://www.oracle.com/technetwork/server-storage/solaris11/overview/solaris-matrix-1549264.html
Note - Oracle VM Server for SPARC 3.1.1 requires firmware version 8.4.2.d. Oracle Solaris 11.1 SRU 17 contains Oracle VM Server for SPARC 3.1.1.
Table 1-2 Supported Versions of the Oracle Solaris OS and Firmware