Asif,
I'm not sure I entirely understand the specific use-case you describe, but there is no problem setting up Oracle Streams or Oracle GG replication between VDBs. The need to test replication solutions, along with all functionality, is not affected by the "virtual-ness" of a VDB.
VDBs are independent Oracle databases and instances with their own DBID, GLOBAL_NAMES, and other attributes important to any replication solution. The only difference between a VDB and a "physical" database outside the influence of Delphix is that the storage of a VDB is actually located on the Delphix appliance using NFS, so only issues related to the storage of datafiles, tempfiles, controlfiles, online redo logfiles, archived redo logfiles, and such are affected.
Hope this helps!
-Tim Gorman