On a recent oracle forum dicussion which started of with the title "Multiplex redo log files?" but really with the question "Is it a normal operation to backup redo log files as well ?", I put in a response to the "normal" assertion to "never backup redo logs".
There's probably no documentation that "says to include online redo logs as part of a backup".
However, there are situations where you _can_ (or even would want to) include your redo logs in a backup. Note that I say "a backup", not "backups". A specific, adhoc, backup may include redo logs.
1. I take a cold backup of a database and restore it to another server. I do not wish to do a RESETLOGS (why, I ask "do I HAVE to resetlogs ?"). Then, I include my redo logs in my cold backup and restore.
2. I am testing backup and recovery scenarios. I take a cold backup of the whole database as a "reference point" in all my various recovery tests.
3. I am attempting a recovery of a production database to verify data at different points in time. I know that I might have to also do a resetlogs in between, change the incarnation id, maybe even change the db_name etc. I want to be able to revert to any restored image during the few rounds of restore-and-verify-data. Those intermediate backups would well be cold backups with redo logs (after resetlogs ?)
4. I am remotely advising a DBA on recovery of a crashed database. I cannot be sure that he has verified all the archivelogs, got the current log sequence numbers etc. I know that it is likely that one or more of the online redo logs hadn't yet been archivedand I would be able to "simulate" them as archived logs during the recovery -- but only if I do ensure that the redo logs are backed up.
5. The last one or two archivelogs had not got included in the tape backup. However, since I know that the database has 4 or 5 or 6 online redo logs, those last two are still available "on-disk" in the form of "online" redo logs (which might very well be raw devices, just to make things more complicated), which haven't been "lost" in the filesystem crash.
Bottom Line : As a "general" rule, it is not necessary to backup online redo logs.As a "general" piece of advise, it _can_ be dangerous to blindly backup online redologs, even in cold backups.However, there can be *specific* cases where I know I would want to backup the online redo logs.
Remember that "online redo logs" doesn't mean exactly the same as "CURRENT" or "ACTIVE".