VMware NSX
The "systemctl status snmpd" or "systemctl status vmware-snmpd" just shows the active time for OS level service/process. Output of this command just shows the re-initialized time of SNMP agent.
If there were any changes made in the SNMP config, SNMP agent will be re-initialized as well(but without OS level service/process restart).
There is no OID present for SNMP agent in NSX-T to monitor the uptime of manager/edges.
Hence, the uptime of NSX manager/edges cannot be monitored through any third-party tool.
Refer below KB article to determine the MIB module listing, name, and type of an SNMP OID:-
https://knowledge.broadcom.com/external/article?articleId=313524