If this is a single volume you wish to separate, then yes, using the Volume name field is the easiest and most efficient.
I would question the need to separate it. If the logic is the same as the others and in your examples above, I would suggest changing to the use of Custom Properties (CP) for volume utilisation threshold, as this provides the flexibility you require. For example in this case you would set a 97 value for this volume in the CP threshold in others it might be 95 or 92 or whatever.
A prime rule for alert management - Create as few alerts is possible!
Use of custom properties is key to this, including the use of a CP as the variable for email addresses to allow emails to be sent to different addresses based on the content of the CP for the object that has an issue.
Hope this helps.
Go with a custom property, its good to keep it as generic and simple as possible for you to manage your environment.
You already have that setup rite Alerting_not_required, just set it to NO for this particular volume.
And since you need a specific one you can create an additional Custom property like 'threshold' on the Volume and use it in the new alert, create a new CP if you are expecting more requirements like this, because create a CP for just one requirement doesn't help much. If not, just create a specific alert for that volume alone when condition is > 98% .....