I'm working on a project integrating SAP and Siebel using BizTalk 2004. Last week I discovered that Siebel (By default) generates RPC based web services, and I was wondering why I can't capture the response of these web services using BizTalk SOAP adaptor! Turns out that you need to set the webservice to Doc literal, a setting in the WSDL of the Web service, this is the setting the adaptor supports. I think you would have the same problem using BizTalk with WebLogic Integration or a webservice generated by Integration.
Enjoy!