Unlike most Maven plug-ins, FindBugs is a proprietary tool that stores its data in an xml file which is not generated by default.
In order for the Dashboard to be able to extract FindBugs's results, you'll need to update the FindBugs report in the reporting section of your POM as follows:
WARNING :
<reporting>
<plugins>
...
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>findbugs-maven-plugin</artifactId>
<version>1.1.1</version>
<configuration>
<xmlOutput>true</xmlOutput>
<effort>Max</effort>
</configuration>
</plugin>
...
</plugins>
</reporting>