Hi Raj,
the saphostagent is updated through the same approach, when you use this method through the studio you can also select the latest hostagent. But also when you download it manually both the rpm and sar file versions are available on service marketplace.
When you start the revision update the system basically creates a shadow version you can see this under "/hana/shared/<SID>/exe/linuxx86_64" here you should see a link named "hdb" and a link named "hdb_old". So during the upgrade first a shadow folder is created and when the system is finished it will automatically shutdown the hana instance and then switch these folder and start the instance again.
So it is only a small downtime but still there is always a downtime. Only possible option to upgrade without downtime is when you have SAP Replication Server in place but that includes additional (standby) hardware.
Kind Regards,
Nico van der Linden