This seems to be problem others are having also, hope this helps:
RW 8 Resources > Photos -> “No Photos found” if Photos on external drive, even if set in: Photos > Preferences > Library Location [Ext Drive Name] > Use as System Library.
A work around that I found: In RW Common Resources, create a folder, example - “RW Photo exports.”
Drag one photo from it into Resources.
Then Resources > Project will show path to the new folder. Clicking on it will show all the exported images: You can then select them into your site without importing them all into Resources [ this only shows for current session, but better than cluttering Resources with a large number of images. Next session, just delete previous imported image and reselect it (or another) to recreate the path]