DirLoader isn't what you want, I don't think. That's mostly for pulling very large offline-generated programs into the robot, or memory-swapping to get around the KRC4's (frankly ridiculous) small memory capacity.
You need an actual communications method between the robot and the camera system. Which one depends on what options your robot has, and what your camera system supports. Almost all Cognex machine vision systems, for example, can communicate using ProfiNet or EthernetIP. If your vision system is PC-based, and supports simple communication by strings over TCP/IP, then the EthernetKRLXML (EKI) option option for the robot will make that available. OPC-UA (a subset of the "full" OPC) is possible, but would require adding that option to the robot, and that your vision system support OPA-UA.
As Panic mentioned, there is a method to access text files from KSS 8.x, but this would have a timing issue -- how would you be able to confirm that the file the robot is pulling data from is the one most recently written by the vision system? This is why you need some sort of bidirectional communication with handshaking.
You could try KUKAVARPROXY (look in the forum archives), but it's not a supported product, so might not be robust enough for production.
Also as Panic mentioned, accessing the program files on the hard drive directly is a bad idea. The way KRCs work, is that they load all the operating files from the hard drive during boot, into a RAM drive in the robot's memory. Then, the robot runs from that RAM drive. The files on the hard drive are only updated periodically or on certain events, and the RAM drive is not accessible from the outside.
the project is still under development so I have all the possibilities to develop it in the best way,
what do you advise me to use?