As a plugin developer you can use this plugin as dependency of your plugin by adding a dependency tag to your POM.
To add the latest version of this plugin as a maven dependency, use the following:
<dependency>
<groupId>org.jenkins-ci.plugins</groupId>
<artifactId>external-monitor-job</artifactId>
<version>203.v683c09d993b_9</version>
</dependency>