If you wish to output a report of everything being monitored in your scom 2012 management group via the scom agent then you can use powershell to achieve this.
The short powershell script listed below will output a csv file to the c: drive on the computer you run the script from called scomagentdevices.csv
NOTE:-This does not include agentless or network devices and is for SCOM 2012
SCRIPT LISTED BELOW………………….copy to notepad and save as a ps1 file
#Import SCOM powershell module
#Output list of all devices with a SCOM agent
get-scomagent|select DisplayName|export-csv -notype c:\scomagentdevices.csv