We are co-locating our Exchange Servers and need to have high availability. The current configuration is two clustered Exchange 2007 servers with a separate hub transport/CAS server. The contemplated configuration is two Exchange 2010 servers and two domain controllers configured to DAG. To achieve load balancing can I put the Hub Transport role on the domain controllers? I know best practice is to not to mix the two but this is a small operation, only 100 users. Just trying to avoid buying yet more hardware (a load balancer).