OK. Let's see what the manual tells us,http://docs.oracle.com/cd/E11882_01/bac ... m#BRADV999
"In this scenario, the database is shut down, and all of the data files are damaged. You have image copies of all the damaged data files. You decide to use the existing image copies as the new data files, thus eliminating restore time."
So first thing we need to understand is the database needs to be down. In RAC, this means that all instances need to be shutdown. If any instance is up, then the database is open. You need to keep in mind the clear distinction between instance and database. When you are working with single instance databases, it is easy to consider them the same thing.
Some (but not all) operations will require the CLUSTER_DATABASE parameter to be set to FALSE, for the operation to succeed. In these situations, you will have to switch it back before starting the other RAC instances.