It might be useful to periodically keep track of changes made to the Security-User Roles section of SCOM. You are going to know who you have given the ability to make modifications, but it is not quite as easy to see which of your SCOM Admins has made the most recent change. Good news is you can do this as follows:-
Launch the SQL Management studio and connect to the instance that contains your Operational SCOM Database
Right click the OperationsManager DB and select New Query
Type the following and then click Execute:
The results will be displayed in a table and will show you who made the last modification in the right hand column.