Yes, the external .app requires the other .app which is hidden because there's no reason for people to use it.
I think Sydde's point was "Why don't you just embed the hidden app within the visible app?". An app-bundle can contain other executables, including complete other app-bundles.
If the hidden app is embedded in the visible app, then for users, it appears to be a single app. They can move it, delete it, etc. and never lose the hidden app, because it's embedded in the visible app bundle.
Also, by embedding the hidden app, the visible app always knows exactly where to find the hidden app: in its own app bundle.
I can't immediately think of an example of an app bundle embedded in another app bundle. However, if you look inside Activity Monitor.app, located in the standard /Applications/Utilities folder, you'll see two executables. One is the privileged data-collection daemon.