ImportMetadata_Conversion Tool returns error when run in a standalone Python script of ArcMap. The error states that the "Parameters are invalid" and "Error 00816: The tool is not valid". The code used for the script was created by ModelBuilder and reflects what is found in the documentation for the tool. The documentation also needs to be updated with this bug.
Run the tools inside of ArcMap or ArcCatalogAdd GpMetadataFunctions.dll and MetadataTranslator.dll into the GAC, then the Python script will run fine outside of ArcGIS Desktop applications.