When extracting FSG hierarchies, I typically configure rowsets e.g. an FSG row for each level of the hierarchy.
, decode(axis_set_type, 'C', 'Column', 'Row') AS axis_set_type
The hierarchy logic is built into the FSG definition (from RG_REPORT_AXIS_CONTENTS); the ETL will extract this logic and build a hierarchy kin the warehouse, all you need to provide it with is the axis_set_id(s) (up to 6).
You must configure file_glacct_segment_config_ora regardless of the hierarchy extract method.