If RMAN copy copies the archived redo logs when they are full, what happens to the current redo log in the event of a failure (hardware failure, etc.)? Isn't there always an active redo log that is not an archive_log?
Yes, if the database is open in read-write mode there is always a number of changes to database that reside only in the current redo log and not in any archived log. If you want protect the current redo against hardware-related corruption, you need to add redundant storage (with either a remote replication or local mirror). If you want to protect the current redo from OS-related corruption, you need a "physical standby" database (the marketing term is DataGuard) with "SYNC LGWR" feed.
RMAN would not be useful to you, it is not designed for a a rolling backup of current redo.