hdfs_path refers to any hdfs location (file,directory,symlink etc.,). Since hdfs_path is already registered in Atlas, you can write a hook in hdfs to capture metadata change events and construct the json as per hdfs_path type definition and POST it to Atlas.
Also , you can create your own custom type and register it.
Since you are writing own hook libraries for hdfs , your hook library can construct the json to use the existing type system in 0.7 or your custom type you registered.