I've searched high and low and came to the conclusion that objects created in Photoshop or other programs that have transparent backgrounds don't maintain their transparency in FrameMaker. FrameMaker just turns the background white. Here is a link discussing this issue on another FrameMaker forum. Link: Transparency in FrameMaker 11. I've done all the things that the poster in that forum has done. I would definitely like to see this feature in FrameMaker 13.
Until FM is able to directly output PDF, it just can't happen (transparency). FM uses a postscript process to create output for PDFs, i.e. print to postscript and distill. Postscript doesn't support transparency. Changing the internal engine is a very major undertaking.