Actually, logging into ftp is very important - they will want to view your error_logs, so you should make sure they are available via ftp.
And if it can't read the config.php file, then you have to wonder if it's a php error that is happening. If so, that would be in those error_logs I just mentioned. So, if I were you, I'd make sure your host has enabled error_logging and that the error_logs are right there in the directory or you'll be hearing back with the person asking them where they are.