AFAIK, there is only one way to achieve this. Create two folders under the datacenter - 'Alarm-Required-VMs' and 'Alarm-NotRequired-VMs'. Place the required VMs accordingly in these folders, disable the alarm at the vCenter level (or at the datacenter level - wherever it has been configured currently) and enable the alarms only for the folder 'Alarm-Required-VMs'. As you would know already, you can also disable all the alarms for a specific object such as a VM. However, this will disable all the alarms and there is no option to disable a specific alarm.
Cheers,
Supreet
