Can the Infrastructure (both Metadata Repository database and the Identity Management services) be run on a hardware cluster?
Yes, the Infrastructure can be run on Cold Failover Clusters using standard clusterware such as Sun Cluster, HP MC/Service Guard, Red Hat Cluster Manager, etc (see the certification matrix here for a list of certified clusterwares for each platform) . This is an Active/Passive cluster solution and is fully supported. For even higher availability and for scalability, Infrastructure can be deployed on Active Failover Clusters (AFC). This is an Active/Active solution.