The theory is that since the database was shutdown normal/immediate anyway no media recovery will be needed when the database comes back up. The redo logs can then be re-created if the database needs to be restored.
However, I am of the opinion that with a cold backup I should be able to get the database back exactly as it was when I shut it down.
1. Perform a forced checkpoint and a log switch just before backing up the archive redo log files and backup the database files before the archive log files.
2. Backup the control file before the forced log switch/checkpoint, if you lose your online redo logs you will always have to do an incomplete recovery but the intention is that you will not lose much.
3. Have your logs and archived logs on different physical disks/arrays or you risk losing both the logs and the archives in a single disk/controller/cache failure. Be wary of shared caches on disk arrays and whether they are write back or write through.
A backup of the online redo logs is worthless, they do not contain the current data only the data at the time of backup. You do NOT need them to perform a recovery if you have performed a full backup.