I have a status dashboard for general IT Services such as Exchange, remote sites etc.
Generally most of these groups are pointed at a group of servers etc.
I am using 2010 - is it possible to somehow configure the exchange group so that it also monitors mailbox databases and if a problem change the status of the group monitor to red?
Get me?? 
It sounds like you should probably create a custom group using the class for mailbox databases (I don’t know what this is as I don’t run Exchange), then create a rollup monitor for the group:
https://support.squaredup.com/v3/Troubleshooting/Dashboards/WhatToDoIfAGroupShowsNoHealthInformation
Maybe you can check out this v2 dashboard?
https://community.squaredup.com/browse/download-info/exchange-dashboard-2/
Do you see the status of the mailboxdatabase in scom?
If you see them in a view in scom you can check the scope of that view and use the same group in your dashboard.