Given your situation, if the Poser 8 RT folder was create away from the Programs File folder, then yes, you can use it.  However, if you want to organize your content into categories, then create your own.

Now here is a little tip to save you time and aggravation, at the upper right hand corner of your P8 Library is a folder button with the Poser running man and a + sign.  That button adds more RT folders to your Library.  But you can also create RT folders and Poser will automatically create the necessary internal folders for you.  Click the button and in the resulting hierarchy panel select where you want to situate your new folder, click Create New Folder button at the bottom, and name your new folder.  Click Ok and a new external RT folder is created and added to your Poser Library.