Suppose project A is of type 'pom' and only holds a number of dependencies.
Eclipse won't generate a .project file for such projects.
Project B has a reference to project A. It will check it is part of the reactorBuild (it does) so it adds it as a project.
The plugin should also check if such a reference is a valid eclipse-project.
The easiest and most solid way it to check if the .project file exists.
The order of the reactorbuild is already solved by Maven, so the plugin can just use it.