Microsoft does recomend not to do this! Because they do not like using the NLB !
If you plan to use a NLB use a hardware Loadbalancer!
Also CAS Array will not work with DAG members. DAG members utilize Windows Failover Clustering, which can’t co-exist with NLB!
http://exchangeserverpro.com/how-to-install-an-exchange-server-2010-client-access-server-array