Hi Marc,
yes you can do that making use of the MassIndexerProgressMonitor interface, see also
Code:
/**
* Override the default <code>MassIndexerProgressMonitor</code>.
 * 
* @param monitor this instance will receive updates about the massindexing progress.
* @return <tt>this</tt> for method chaining
*/
org.hibernate.search.MassIndexer.progressMonitor(MassIndexerProgressMonitor)
You could extend 
org.hibernate.search.impl.SimpleIndexingProgressMonitor and override the method 
indexingCompleted() (or just implement your own 
MassIndexerProgressMonitor)