Not sure what you mean by "integrated".  If you mean, "is DataDomain supported as an NDMP VTL for Isilon/", you can check the Release notes for the version of OneFS you're using.  If you're asking if DataDomain is supported as a backup target for Isilon, that will depend on your backup software and configuration.  Let us know if that helps!
Is Data Domain integrated with EMC Isilon?
Data Domain integration with EMC Isilon