Yeah this is a bit confusing. I'd like the ability to do like manager.addShortText(textToDisplay) from a Pipeline Groovy script. It's a bit confusing because this plugin seems to be doing two things, really – its name is deceptive. It provides a way to run Groovy scripts at the end of a build, but it also provides some helpful UI widgets.

This is how the plugin gets its manager – with the right imports you might be able to get it to work in a Pipeline script:

TaskListener listener = new LogTaskListener(Logger.getLogger(WorkflowManager.class.getName()), Level.WARNING);
return new GroovyPostbuildRecorder.BadgeManager(build, listener, Result.FAILURE);

See WorkflowManager.java

Actually, these might be easier to emulate in a Pipeline script:

public void addShortText(String text) {
  build.getActions().add(GroovyPostbuildAction.createShortText(text));
}

public void addShortText(String text, String color, String background, String border, String borderColor) {
  build.getActions().add(GroovyPostbuildAction.createShortText(text, color, background, border, borderColor));
}

Those are from GroovyPostbuildRecorder.java

The import needed is org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildAction

The build is available as currentBuild.rawBuild in Pipeline Groovy scripts.

Hi Tyrel Haveman, sadly the GroovyPostbuildAction.createShortText method is not whitelisted so it cannot be executed from the pipeline it gives a: 

org.jenkinsci.plugins.scriptsecurity.sandbox.RejectedAccessException: Scripts not permitted to use staticMethod org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildAction createShortText 

This method cannot be approved in the Script Approval.

I think this is not a minor priority task. This ability, along with the new pipeline syntax are very useful and practical.

Hello Jonas Thyregod,
The workaround proposed by Tyrel Haveman worked for me. My pipeline script looks this way:

import org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildAction;
node ('myNode') {
...
  stage ('Post-Build') {
    currentBuild.rawBuild.getActions().add(GroovyPostbuildAction.createShortText("text"));
  }
}

Jenkins: 2.73.3
Groovy PostBuild Plugin: 2.3.1

The content of the approved methods ("Signatures already approved:"):

method hudson.model.Actionable getActions
method org.jenkinsci.plugins.workflow.support.steps.build.RunWrapper getRawBuild
staticMethod org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildAction createShortText
java.lang.String

Badge and summary features are extracted to badge-plugin: https://github.com/jenkinsci/badge-plugin/blob/master/README.md
You can use those features also in pipelines. Please try that.