RMAN is doing the same trick at the DF level. when RMAN do the copy file, it's like hot backup.

actually, in metalink, there is an internal note about how to use RMAN backupset if the control file is corrupted and unrecoverable. So essentially, controlfile is not needed, all needed is the extracted datafiles from the backupset.

In my experiment, one more complication is the RAC ASM -> non-RAC/non-ASM. The data files are all magic numbers generated by Oracle Managed files. When I do the DB refresh, I will stop the Standby DB apply (non-RAC/non-ASM). and copy the DFs over. This provides consistency during the copy.