Is dependency-reduced-pom.xml automatically used instead of pom.xml?

The dependency-reduced-pom.xml is generated at build time into ${basedir} of the project. This file is a temporary file that is only used for packaging into the shaded jar. Quoting the documentation of the createDependencyReducedPom attribute:

Flag whether to generate a simplified POM for the shaded artifact. If set to true, dependencies that have been included into the uber JAR will be removed from the <dependencies> section of the generated POM. The reduced POM will be named dependency-reduced-pom.xml and is stored into the same directory as the shaded artifact. Unless you also specify dependencyReducedPomLocation, the plugin will create a temporary file named dependency-reduced-pom.xml in the project basedir.

To make it clear, after the maven-shade-plugin has run:

• your initial POM will be left unchanged;
• a temporary file that you can completely ignore named dependency-reduced-pom.xml will have been generated inside the root folder (this is considered an open issue with this plugin);
• the shaded artifact will contain your initial POM unchanged inside the META-INF directory and not the reduced POM (this is not really important but better mention it – there was an issue about this that was closed automatically: MSHADE-36);
• the POM that will be deployed is the reduced POM;
• the shaded artifact will be by default the main artifact of the project.