Drupal - How to hide the content of nodes/ completely, and still maintain use within Drupal?

There are two Drupal modules that offer this functionality:

• Rabbit Hole
• Internal Nodes

Johan Falk of nodeone.se just reciently did an excellent video series on Page Manager (part of cTools, a very common module) and he covered a use case like you are describing very well. link.

Basically you set up a variant in Page Manager and have the response be a http request code (probably a 301 in your case) to redirect to your intended destination. In his example (I think it was the 2nd or 3rd video in the series, they are all pretty quick though) he was using node references and he didn't want anyone to get to a 'sub node' but redirect you to the parent node if you tried to access it. Your use case sounds like it could be even simpler, just have anyone trying to access one of your slideshow nodes redirected to page that shows the correct full slideshow.

You don't even need panels to get all of this magic to work. And you can get pretty complex in your redirect rules if you have stuff like node references installed to load related nodes.