The T8-2 has two internal HBAs that provide access to 4 resp. 2 disks. These HBAs are on separate IO controllers, so it should be possible to boot two independent domains from internal disks.
Unfortunately though, all 4 network ports are on the same root complex. In order to have a completely independent secondary domain, you would have to provide an additional network card.
Take a look at the T8/M8 Architecture Whitepaper: Oracle's SPARC T8 and SPARC M8 Server Architecture (pages 19 and 20). If you have MOS access, also take a look at note 1005907.1 (SPARC Platforms: Matrix of Recognized Device Paths)