Hello,
That's correct, if you set up the Performance Management > Performance Option > Default Monitoring Indexes in advance of discovering devices, and you configure the Monitor Option (also under Performance Option) accordingly, then all newly added devices with interfaces that match the Monitor Option configuration will automatically have the performance monitoring indexes you've selected as default added to matching interfaces.
Monitor Option in-context help provides some details about the way it determines what to monitor:
You can select only one option from the following:
All interfaces,
Up interfaces,
Monitor Physical Interfaces only,
UP Physical Interfaces.
You can select one or multiple options from the following:
Interfaces Connected to SNMP Devices,
Interfaces Connected to Servers,
Interfaces Connected to PCs.
The three options are ORed. The first four options and the last three options are ANDed. For example, when you select Monitor Up-Interfaces only, Monitor Interfaces Connected to SNMP Devices, and Monitor Interfaces Connected to Servers, the interface index will monitor the UP interfaces connected to SNMP devices and servers.
For example, if you choose 'All Interfaces' and 'Interfaces Connected to SNMP Devices', and then discover a device, iMC will automatically add your default interface performance monitoring choices to all interfaces (including virtual ones) on the newly added device where iMC detects a link to another managed SNMP device.
Be careful not to un-check all the "Interface Connected to ..." boxes. If you do that and have 'All interfaces' selected, then iMC adds the default interface performance monitoring to every singly interface on the newly added devices, regardless of link type. If you add a lot of devices like this, it can cause significant load on iMC and degrade its performance. Normally you only want to monitor inter-switch interfaces, and perhaps interfaces connected to servers - hence the Interfaces Connected to SNMP Devices and Servers options are checked by default and recommended to avoid excessive monitoring.
Hope that helps explain how to add interface monitoring by default.