Taken directly from the website:
Sometimes the question "how can I monitor multiple farms with the SharePoint 2010 management pack" comes up. The guide says that the MP only supports one farm - but there is a straightforward way to help the MP manage multiple farms.
A file named SharePointMP.config is used to configure the behavior of the SharePoint 2010 management pack. This file should be on all RMS roles in the given management group Icluster case).
The challenge with monitoring multiple farms is due to the need to have farm administrator permission to do the discovery and monitoring that is used to monitor SharePoint 2010. The typical configuration for a single farm has the SCOM admin assuming that the run-as profile is involved and directly manipulating this is a complex operation for multiple farms.
The config file and configuration task included in the MP comes to the rescue here.
That file contains a section called Associations. It is this section that should be adjusted for multiple farm support.
<Association Account="Contoso - SharePoint Farm administrator -3" Type="Agent">
<Association Account="Contoso - SharePoint 2010 Farm Administrator 2" Type="Agent">
<Association Account="Contoso - SharePoint 2010 Farm Administrator" Type="Agent">
After adjusting the SharePoint configuration file, run the configuration task that is included in the management pack per the instructions found in the guide.
The related thread can be found here.