@Eduardo_Curonisy In the first case you provided, you are using version 2.2.1 of ES-Hadoop which can only interact with earlier versions of Elasticsearch (2.2 and below). So you are correct in that you need to upgrade to a newer version of the connector.
I would avoid using the *-alpha releases of the connector at this point. ES-Hadoop is released in lock step with Elasticsearch now, so version 5.2.2 is already out and will be the most compatible with your version of Elasticsearch. Generally, it's best to keep ES-Hadoop at the same version or higher (we support backwards compatibility).
It was also discovered early in the 5.0 release cycle that a change in the build process meant that Scala classes in the Spark package were being compiled for Java 8 instead of in compatibility mode for Java 6. This was fixed and should be correct in version 5.2.2.