Although the command in your script are SQL I don’t think there’s an equivalent command in the DBML syntax and are not needed in order to draw a database diagram. Remove or comment out lines 29, 31 and 33 in your script.
I found that all ... OWNER TO ... and ... OWNED BY ... statements caused the importer to choke. I’m not a PostgreSQL expert by any means, so I don’t know how important these statements are - I just stripped them out of the import and everything worked fine.