hmmm...
there might be a way..
as i recall the Document.fonts collection includes the fonts from EMBEDDED vector files, but there is no way of telling the difference between one used in a vector file and the one used by the document itself.
so the solutions is "simple"..
collect all your vector links (doc.allGraphics, and then test each link for the type, to see if it's a vector)
copy them to a new BLANK document
embedd them
alert myNewDoc.fonts.everyItem().name.join('\r')
bingo!
can't realy write the script right now, but it should get you in the right direction.