When you discover a Solaris Cluster, you're asked to provide ssh credentials and JMX credentials. You already know the ssh credentials but what about those JMX credentials? They're for the agent on the cluster's global node. The agent uses JMX so they're called JMX credentials. Think of them as agent credentials.
The only thing these credentials are doing is allowing the agent on the global node to respond to the Enterprise Controller. Without the JMX creds, you can discover and manage the cluster server itself, but nothing else. If you look in the log file, you'll see a message like "JMXMP provider exception java.net.ConnectException: Connection refused." With the JMX creds, Ops Center authenticates the agent, connects to the agent, and acquires all the agent's information about the global node.
JMX credentials can be anything convenient for you, like cluster1 and cluster2, and simple passwords. For all global nodes to use the same credentials, create one set in the discovery profile and run the discovery job. However, if for some reason, you need to use a unique set of credentials for each global node, create each set of credentials in a credential profile and then run a discovery job for each global node. You'll use the same discovery profile but change the credential profile for each job. You can still keep it simple, like cluster1node1 and cluster1node2.