Instant Messaging supports the use of load balancers located in front of the Instant Messaging multiplexors. However, you cannot currently use load balancers between the Instant Messaging multiplexors and the Instant Messaging server.
When deploying Instant Messaging as part of a Portal Server/Secure Remote Access deployment, you can locate load balancers between the Secure Remote Access gateway and the Instant Messaging multiplexors.
If you just need security for the client connection, and not HTTP tunneling, consider using SSL instead of Secure Remote Access. You can configure a secure Instant Messaging client connection by enabling SSL on the multiplexors and locating them outside the firewall.