Now I understand but unfortunately I don't know how do it :smileyhappy:.
When you create local users, they have email value. Did you try to fill in this value, configure SMTP Server on vCenter and catch some event by vCenter Alarm or SNMP trap?
If it is possible to catch such event by SNMP, you could send email notification by external system.
Unfortunately, I don't have possibilities to test it :smileysad: