Has anyone had any problems with Nagios taking out a server or switch on your network.
Short Answer: No.
Slightly longer answer: It could mess things up. One way I could see this happening is if you do an eventhandler that does a reboot of the equipment and the equipment does not reboot properly. Another possible way you could mess up a piece of equipment is through SNMP. Again, as in the reboot scenario above, you will need to do an eventhandler that uses the RW community string to set a value via SNMP. If that value or the OID is wrong you could set something you did not expect.
Also, SNMP is not secure, so if you can, do not allow a device on your network that has SNMP enabled be accessible via a public IP address. By default SNMP uses the community string ‘private’ for RW and ‘public’ for RO. If you do not change the RW string someone could make changes to your equipment remotely. In fact I would suggest that you disable any RW SNMP community string you have, since SNMP is not that secure to begin with.
Hope that helps