Recently Microsoft released a hotfix for Forefront UAG and applies to multiple Forefront UAG server scenario configured in an Array configuration.
Link Local ISATAP addresses are not created for the virtual IP address used by the Network Load Balancing (NLB) feature on a computer that is running Windows Server 2008 R2. This hinders the usage of NLB nodes as an ISATAP router.
This problem occurs because the IP Helper service does not let virtual IP address interfaces generate ISATAP tunneled addresses or 6to4 tunneled addresses as designed. For the DIP address ( Dedicated IP ) you will have an ISATAP address available but for the VIP ( Virtual IP ) there is no possibility of having Global Addresses support for the NLB VIP address ( Virtual IP) and no ISATAP addresses can be configured for a VIP.
More information can be found here