Steps to perform pg_dump on Postgresql RDS instance

change_owner.sql

alter schema schema_name1 owner to rds_superuser;
alter schema schema_name2 owner to rds_superuser;
\dn;
CREATE FUNCTION exec(text) returns text language plpgsql volatile AS $f$             
BEGIN EXECUTE $1; RETURN $1; END; $f$;
SELECT exec('ALTER TABLE ' || quote_ident(s.nspname) || '.' || quote_ident(s.relname) || ' OWNER TO rds_superuser')
FROM (
SELECT nspname, relname
FROM pg_class c JOIN pg_namespace n ON (c.relnamespace = n.oid) 
WHERE nspname in ('schema_name1', 'schema_name2') AND
      relkind IN ('r','S','v') ORDER BY relkind = 'S')
s;

pg_dump Postgresql RDS

Update the change_owner.sql script with the relevant "rds_superuser" and "schema_name"
Connect to RDS instance through psql prompt and run the change_owner.sql script

External reference:
http://stackoverflow.com/questions/4363697/copy-a-postgres-database-without-lock-permissions
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.PostgreSQL.CommonDBATasks.html#Appendix.PostgreSQL.CommonDBATasks.PostGIS