restoring database using RMAN
No. RMAN is aware of that possibility, hence why it creates a snapshot controlfile before performing backup. Rman needs to access control file to map objects to be backed up, and as controlfile is always in use, snapshot is used for that specific point in time. When you restore a backup, you're simply telling oracle to place those files from the backup back, so you don't need to worry about your data getting overwritten.