Nimbostratus
Employee
Not sure if I am hitting the mark with this response but here goes. You can definitely LB the LDAP servers and monitor them specifically. If I am understanding, the Open Systems may try to use a LDAP server that is unavailable. You can use LTM to load balance the LDAP pool and assign an LDAP specific health monitor to the pool and/or nodes to ensure that traffice is directed to only available servers.
You can create a custom LDAP monitor at: 'Local Traffic' --> 'Monitors' --> 'Create' & select 'LDAP' for Type.
Here's a link to AskF5.com that discusses LDAP monitoring best practices:
http://support.f5.com/kb/en-us/solutions/public/9000/300/sol9311.html?sr=18473158
Hope this helps...
Greg