Is this the IDEA Plugin that allows me to run Maven commands from within IntelliJ IDEA?

No. This is a Maven plugin to generate IntelliJ IDEA files for a Maven project. This is not an IDEA Plugin for Maven.


How does the IDEA plugin work on multi-projects?

Maven IDEA Plugin, by default, creates the project file (*.ipr) and the workspace file (*.iws) from where the root pom is located. Then module files (*.iml) are created for each of the projects inside the reactor.

If some projects depend on another project in the reactor, then the reference to the project is given instead of the hard-references to the local repository copies of the artifacts.