Using a cluster as a target for agent-to-agent tests will work fine, unless all agents are behind the same NAT. In this scenario, you'll need to create a firewall rule for the target, which would point to a specific agent in the cluster. While all results will behave as planned, the agent targeted will absorb all agent-to-agent tests targeted at that specific port on the cluster. To target different agents, change the port of the target, which is set under the Advanced Settings tab of the test's configuration.