The LDAP iApp is for load balancing LDAP resources. Are you saying that your devices won't be able to perform bound LDAP queries, so you want the F5 to proxy the LDAP requests, as in BIND and perform the queries on the device's behalf?
Have you considered enabling anonymous LDAP queries to AD (http://windowsitpro.com/active-directory/q-how-do-i-enable-anonymous-ldap-binds-windows-server-2008-active-directory-ad)? Otherwise, the best option is to use the Access Policy Manager module (APM) to perform an LDAP bind and proxy.
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