A couple things.
1. you can bring a .swf file into FCP no problem.
2. You said you hand regular NTSC 720×480 footage. You need to work in the frame size of you smallest size media.
So what I would do is:
1. capture the HDV footage natively (make sure it’s set to anamorphic) create a matching seq and put it in.
2. then create a 720×480 NTSC seq (non anamorphic). Put your p30 in there, and drag the HDV SEQ into the NTSC DV timeline.
3. bring stills into the timleine.
4. make flash at 720×480 (make sure to compensate for title safe) and bring it in also (.swf or .mov)
hope this helps