I think that you are looking to provide a "LOCATION" for your database on DBFS. When you provide a location for your database all the tables will be created within that folder by default.

See a create table example below:

CREATE TABLE [ IF NOT EXISTS ] table_identifier
  [ ( col_name1 col_type1 [ COMMENT col_comment1 ], ... ) ]
  USING data_source
  [ OPTIONS ( key1 [ = ] val1, key2 [ = ] val2, ... ) ]
  [ PARTITIONED BY ( col_name1, col_name2, ... ) ]
  [ CLUSTERED BY ( col_name3, col_name4, ... )
      [ SORTED BY ( col_name [ ASC | DESC ], ... ) ]
      INTO num_buckets BUCKETS ]
  [ LOCATION path ]
  [ COMMENT table_comment ]
  [ TBLPROPERTIES ( key1 [ = ] val1, key2 [ = ] val2, ... ) ]
  [ AS select_statement ]

The default location of a database will be in the /user/hive/warehouse/<databasename.db>. Irrespective of the location of the database the tables in the database can have different locations and they can be specified at the time of creation.

Database location and Table location are independent. A table can be created in any location. So to answer your question, it's possible to create a sub-directory and create tables in that.