Check the .htaccess file first, and the Settings > General area first to make sure it’s not a level of security-by-obscurity that one of the initial users tried to implement.
The easiest way is to change the name of the folder then see if your site breaks, since you can rename a folder a lot faster than moving directories, deleting then re-uploading, etc.
You could also get a clean WP and check what the core file names are, then make sure that none of the /proc folder content matches that (or it still exists in the core folders in your installation).
I’d have to recommend to start documentation for the site, that way if someone works on it after you they won’t be scratching their heads in confusion either. 🙂