From gradle build, you can set the ant properties, for example. the ant classpath in the following target can be set in gralde build.
<enunciate basedir="${enunciate.baseSourceDirectory}" configFile="enunciate.xml">
<include name="**/*.java"/>
<classpath refid="enunciate.classpath"/>
<classpath>
<pathelement path="${enunciate.dependencies}"/>
</classpath>
<export artifactId="docs" destination="${enunciate.destinationDirectory}/some-icd.tar"/>
In build.gradle, "enunciate.dependencies" can be set as ant.properties['enunciate.dependencies']=configurations.runtime.asPath
I hope this helps.