Bottom Line: Based on working with the Premiere Elements 9 trial version, it appears that you do not need Photoshop Elements 9 installed on the same computer as Premiere Elements 9 in order to be able to use the Watched Folder feature in Premiere Elements 9. For Premiere Elements 8, you had to have Photoshop Elements 8 installed on the same computer as Premiere Elements 8 to get a functioning Watch Folder feature in Premiere Elements 8.
Also, please refer to April 2010 "Watched Folders" thread here where the topic was gone over for Premiere Elements 8.0/8.0.1.
There is a feature called Watched Folders which provides for the automatic placement of media in the Elements Organizer when the media are placed into a hard drive folder designated in the Watched Folder dialog.
You name that folder or folders in the Watch Folders dialog gotten to via the route Elements Organizer File Menu/Watched Folders. But in order for that Watch Folder dialog to be available you need to have a specific activated file in Control Panel/Administrative Tools/Services. For version 8, it is “Adobe Active File Monitor V8”, and, for version 9, it is “Adobe Active File Monitor V9”.
Now you can install JUST Premiere Elements 9 and have the specific “Adobe Active File Monitor V9” be present and activated to make the Watched Folder dialog available for use
(a) Click on the Organizer Tab in the row above the line up Organize Edit Disc Menus Share
(b) In the Elements Organizer, go to File Menu/Watched Folders
(c) If any problems, check the "Adobe Active File Monitor V9" status in Control Panel/Administrative Tools/Services.