Hello Laurence
We removed imagex from GSS quite a while ago. We use ghost which produces gho files. DISM is also another tool to create images and is part of the ADK package from Microsoft. Since Imagex or DISM are not our tools for imaging, support for them is beyond the scope of Broadcom Support.
With that said you may be able to locate imaging tool and place it in the imaging directory and script its usage. You will need to also edit the ImagingTools.ini file and add the imaging tool so it will be listed for usage with in the console. The ini file will walk you through the addition of adding your imaging tool
Hope this clears thing up
Scott Andreas
Broadcom Technical Support