NPM can monitor a wide range of network devices and infrastructure, including routers, switches, firewalls, servers, and virtual machines. However, some devices may not support standard protocols such as SNMP or WMI, or may have specific metrics that are not monitored out-of-the box by NPM. In such cases, you can extend NPM's monitoring to non-standard devices by using object identifiers (OIDs) organized in management information bases (MIBs). OIDs are numeric strings that uniquely identify a variable in a MIB.
MIBs are hierarchical databases that define the properties and values of the variables that can be monitored on a device. By importing device-specific MIBs into the SolarWinds MIB Database, and creating custom pollers based on OIDs from the MIBs, you can monitor any metric that is available on the device. You can also display the polled data in the web console using dedicated or existing resources12. References:
Create custom monitors in NPM - SolarWinds
SCP Study Aid - SolarWinds (page 10)

The Universal Device Poller (UnDP) is a feature of SolarWinds NPM that allows you to create custom monitors for almost any statistic provided by SNMP based on its Management Information Base (MIB) and object identifier (OID). An OID is a unique identifier for a variable that can be polled or set via SNMP. The UnDP retrieves management data in the OID format from the devices that support SNMP. The other formats (WMI, XML, ANSI 1) are not used by the UnDP. References:
Monitor custom statistics based on OIDs with Universal Device Pollers
NPM Universal Device Pollers

The Discovery Ignore List is a feature that allows you to specify the IP addresses or hostnames of the devices that you do not want to monitor or discover in the future. You can add devices to the ignore list manually or automatically during the discovery process. Once a device is added to the ignore list, it will be skipped by any subsequent discovery. You can also remove devices from the ignore list if you change your mind and want to monitor them later. References: Add devices to the Discovery Ignore List in NPM, Remove devices from the Discovery Ignore List in NPM, How to View Devices on Your Windows Network and What to Do If You Can't See Them

Alert suppression is a feature that allows you to create conditions that prevent an alert from being triggered or sent if certain criteria are met. This can help you avoid receiving multiple or unnecessary alerts from a single event or a complex situation. For example, if you have a router that connects your SolarWinds server to a remote site with critical devices, you may not want to receive alerts about those devices if the router is down, as the problem is not with the devices but with the router. In this case, you can configure alert suppression to suppress the alerts for the devices if the router is down. To do this, you need to select the option "Suppress the alert if all of the following apply" and add the conditions "Node Name is equal to 'target'" and "Node Status is equal to 'Down'". This means that the alert will be suppressed only if both conditions are true, i.e., the router with the name 'target' is down. If the router is up or has a different name, the alert will not be suppressed. References: Alert suppression - SolarWinds; Alert Suppression - Forum - Network Performance Monitor (NPM) - THWACK