VMware HA is used in the event when any of the hosts inside a cluster fails then all the virtual machines running under it are restarted on different host in the same cluster.

Now HA is dependent on vMotion to perform live migration of the vms to different host so vMotion is just used for the migration purpose between multiple hosts which is also used by other functionality like DRS.

NOTE: Anyhow HA can WORK very will WITHOUT vMotion as its PRIMARY functionality is to restart the vm from the affected host to the WORKING host but this will be service affecting as the vms will be 'powered off' and then 'powered on' on the new host.

VMware HA is used in the event when any of the hosts inside a cluster fails then all the virtual machines running under it are restarted on different host in the same cluster.

Now HA is dependent on vMotion to perform live migration of the vms to different host so vMotion is just used for the migration purpose between multiple hosts which is also used by other functionality like DRS.

NOTE: Anyhow HA can work very will without vMotion as its primary functionality is to restart the vm from the affected host to the working host but this will be service affecting as the vms will be 'powered off' and then 'powered on' on the new host.