Error exporting data from Oracle to shp using ogr2ogr

No, gdal doesn't generate any user.

You should find '-> "OCI" (read/write)' in the Supported Formats list if "OCI driver" is installed/configured properly. At this point the following syntax (you have to customize a little bit) should work:

ogr2ogr <srs> -f "ESRI Shapefile" /favourite/path/test.shp OCI:"<oracle user>/<oracle password>@(DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = <hostname>)(PORT = <port number>)))(CONNECT_DATA = (SID =<sid name>))):<oracle schema>.<oracle table>"