Correct me if I'm wrong, but out of the box, IRAD 6 only supported the Struts portlet using the old JetSpeed API.
Try to add struts support with a JetSpeed, legacy portlet project with IBM's Rational Application Developer, and you might see the WYSIWYG wizards.
Are you starting from scratch? If you are, I might recommend the JSF portlet framework from IBM. It's my impression that IBM is much more focussed in supporting the Java Server Faces framework, as opposed to the Struts framework.
By the way, I've got a few tutorials on creating JSF and Struts portlets using IRAD on my website. I use the Apache bridge, as opposed to the IBM infrastructure, but the fundamentals are the same. Check out my signature links.
Download the war files as per instruction. Import the SPFStandardBlank.war in RAD. SPFStandardBlank.war is a blank struts JSR 168 portlet project. Develop your application on top of this blank portlet.