I've used similar programs as well that "watch" a folder. I don't think Aperture does this. It tracks referenced files upon import. If I add files to the destination folder outside of Aperture I don't think it will index that folder and show those photos.
I've used both iView Media Pro (now discontinued) and Portfolio Server and they operate on indexed folders as one method of tracking as well as during the import process. What I'm trying to find is the file size of a project for both referenced projects and those stored inside of Aperture. I am burning my Projects to DVD for archival for now and would like to know when I'm reaching that DVD capacity.