The standby controlfile created ('alter database create standby controlfile '/tmp/SID_stdby.ctl') knows these details as from which archive log it has to recover . Here fal_server and fal_client would do the job for you to fetch the log files from primary to standby . And 'alter database recover managed standby database disconnect from session ' starts the recovery process .
How shall I recover the Standby database using the archive files generated while taking hot backup of primary
Generally when i took hot backups for creating standby database purpose , I used to take only backups of the data files. After issuing end backup, I use to create the standby controlfile in the primary database which would have all the archive log file details that generated during the hot backup.
(Not sure how this will work as the SCN in datafile header and control file differs in Hot backup)
I believe that the above command is required only if the controlfile created has not recorded the log files required for recovery. In that case register the logfile and issue the recovery command. If I'm correct you could find out that from standby alert log files. after issuing the recovery command it would be doing 'nothing'.
ALTER DATABASE REGISTER LOGFILE file_specification