Hi HomerJ,
Unfortunately HP doesn't support multiple LDAP servers in ALM 11.52. They haven't supported it since QC10 and more current versions up to ALM 12,2X. If you would like to upgrade to ALM12.2x or later versions they have coded the ability to add multiple LDAP servers within the settings.

Another option you may have is to set up a catalog and use that as your LDAP server URL (this would have to be accomplished by your IT and LDAP admins (as referenced to in this post: http://eyeontesting.com/questions/845/configure-qc-10-to-use-multiple-ldap-servers.html).

At this time there is no support for multiple LDAP servers in ALM11.52 and since the product is reaching end of life there will be no new added features. If this is something that is needed and desired the resolution would be to upgrade your version of ALM to one of the latest versions.

Hope this helps,
Dan