To test Sibel applications with RFT, please follow the below steps.
1. The steps mentioned at the link below are mandatory :
2. The steps and registry key settings mentioned at http://pic.dhe.ibm.com/infocenter/rfthelp/v8r3/topic/com.ibm.rational.test.ft.doc/topics/SiebelJava.html
3. Make sure the browser enablement test passes via RFT's enable environment wizard.
One more resource to consider while you are planning to automate the Siebel testing.