Though i dont use frontrow at all anymore, I did play around with it a little when I was running tiger and it does grab your iTunes content, but it also goes through your movies folder in your user folder.
Because I did use an alias for that then, though it may have been for each individual movie I cant recall.
However another option would be for you to find the movies you want, then drag them into iTunes while holding the option key (I think, but it may be the command key) and it will add the movie to iTunes without actually copying the video into your iTunes folder