Below are the workaround options.
Let CA APM to do the user check based on an order, ldap1 and then ldap2.
Use Introscope EnterpriseManager-LDAP authentication, add 2 realm sections for each LDAP servers.
Securing Introscope using LDAP
Let CA APM to use the authorization features from EEM:
Use Introscope Enterprise Manager -EEM authentication, add two realm sections for the same EEM server, but configure it so that each section uses a specific Admin user for their specific region (Region A / Region B).
Configuring CA EEM authentication using LDAP