I just realized, after much pre-deployment fretting, that it is very simple to assign multiple action accounts to the Active Directory Management pack. Domain controllers in different domains need different action accounts for Active Directory monitoring to work.
Here is how you do it:
1. Go to OpsMgr console>Administration>Security>Run As Accounts.
2. Create an new action account for each of the domains that you will be monitoring. Use “windows” as the type, and be careful typing the password, they are not validated in this field.
3. Go to Administration>Security>Run As Profiles and double click AD MP Account. Click on the Run As Accounts Tab
4. Associate the account to each domain controller by clicking on New… You must manually select each domain controller and choose an account on a by-machine basis.