SOA Suite R12 has not been released yet. I think what you want to know is how to integrate Siebel 8.1 using SOA Suite 11g...
If my guess is correct, the following materials would be helpful for you.
# This documents targets 184.108.40.206 but explanation in this documents is valid in 220.127.116.11.
Oracle® Fusion Middleware Application Adapter for Siebel User's Guide for Oracle WebLogic Server 11g Release 1 (18.104.22.168.0)
# You can download sample projects when clicking the link of "Siebel Adapter Samples" on the following web page.
Packaged Application Adapter Samples: (Official Oracle SOA Suite 11g Samples)
# This video shows how to configure Siebel Adapter on OSB. Even if you want to use BPEL or BPM, configuration procedure is similar to this video and you could configure Siebel Adapter by reference to it.
OSB and Siebel Adapter: (Official Oracle SOA Suite 11g Samples)
Hope this helps.