All the users are distributed across multiple LDAP server, you need all of them to able to access the Introscope workstation.
Does the Enteprise Manager support authentication with more than just one LDAP server?
Yes, you can define multiple LDAP servers by adding multiple descriptors in the EM_HOME\config\realms.xml, for example:
<realm descriptor="LDAP Realm" id="LDAPserver1" active="true">
<realm descriptor="LDAP Realm" id="LDAPserver2" active="true">
For more details about Securing Introscope on each single LDAP instance, please refer to the APM wiki documentation site > "Securing Introscope using LDAP" section.