Amazon RDS Ola Hallengren
The stored procedure DatabaseBackup is not supported on Amazon RDS.


As you note, there is logic that checks for the RDS platform. 

If these checks return that your server is an RDS instance the following code block is encountered. 

  IF @AmazonRDS = 1
  BEGIN
    SET @ErrorMessage = 'The stored procedure DatabaseBackup is not supported on Amazon RDS.'
    RAISERROR('%s',16,1,@ErrorMessage) WITH NOWAIT
    SET @Error = @@ERROR
    RAISERROR(@EmptyLine,10,1) WITH NOWAIT
  END


Pretty self explanatory, eh? Sorry about that 

You're probably best served starting by browsing AWS docs for SQL Server backups on RDS