Geant4 is independent of any histogramming package. The Geant4 toolkit has no drivers for histogramming, and no drivers are needed in Geant4 to use a histogramming package. The code for generating histograms should be compliant with the AIDA abstract interfaces for Data Analysis.
Consequently, you may use your favourite package together with the Geant4 toolkit.
Please refer to the JAS documentation on histogramming for using the JAVA Analysis Studio tool.
Please refer to the PI (Physicist Interfaces) project pages on histogramming for using an AIDA Interactive Analysis Environment.
Please refer to the Open Scientist Lab documentation on histogramming for using the Lab Analysis plug-in for the OnX package.