QuickTime can only open some interactive swfs. Most newer interactive swfs will not work, in my experience. I'm not sure when Apple stopped updating QuickTime's Flash support. I guess it was with QuickTime 5 or 6.
If you want to play flvs in QuickTime, you need
Perian. You might also want to use
Perian's Type Installer to automatically make QuickTime accept flvs.
I've never actually seen flvs encased in swf files, so I can't comment on that.