It depends on the connector. Oracle Loader for Hadoop runs on the Hadoop cluster, and does not reside on the Oracle Database. It can reside on a node from where you submit your map reduce nodes - which might or might be a node on the cluster. Oracle Direct Connector for HDFS resides on Oracle Database.
if I deploy Oracle Direct Connector for HDFS on machine which Oracle Database reside on.
how Oracle interactively call Hadoop which resides on remote machines?
i.e. what the *$HADOOP_HOME* env variable will be set?