You are right that what you are trying to do is not possible. They are after all two different clusters. Just because they both use Kerberos to authenticate doesn't mean you can have one client run query that spans two different clusters and reads data from two different clusters. That is not possible by default.
If you would like to do something like that, then you a data virtualization software. Something like Cisco Information Server or Denodo. the open source data virtualization software is also available as Teiid by JBoss. Without using one of these tools, it is not possible to run one single query that reads data from two different clusters. Think about this way. If you have two different Oracle Systems which have the exact same way to authenticate, can you run a query that reads data from both Oracle systems? Answer is no, at least not without these virtualization tools. Same with Hadoop.