Recently had a request to put an individual Exchange database into maintenance mode as some alerts had triggered for it and there was some planned work scheduled to happen.
I found the easiest way to place an individual object into maintenance mode in SCOM was as follows:-
1. Open the alert that you want to suppress the alert for and view the source of the alert
2. Create a group which contains the source of object which you want to place into maintenance mode
3. Open the group in diagram view
4. Put the group into maintenance mode