For Oracle Databases the name can be up to 8 characters (http://docs.oracle.com/cd/B19306_01/server.102/b14237/initparams052.htm); Delphix does follow Oracle naming conventions of Database Names, however VDBs can have longer Database Unique Names- this can allow you to better identify your VDBs. We have found 30 characters for the Database Unique Name (found on the first step- Target Environment, of "Provision a VDB" card) and the VDB Name (found on step 2- VDB Configuration, of "Provision a VDB" card)- does not seem to have a limit.