i guess cluster manager is part of oracle paralle server a quick searching of oracle docs tells u this.check this on the oracle docs which says

Cluster Manager
The Cluster Manager (CM) monitors process health, specifically of the database instance. LMON, a background process that monitors the health of the Integrated Distributed Lock Manager, registers and de-registers from CM.

It is critical that all Oracle Parallel Server instances receive the same membership information when events occur. Notification changes cause relevant Oracle Parallel Server recovery operations to be initiated. If any node or instance is determined to be dead or otherwise not a properly functioning part of the system, CM terminates all processes on that node or instance. Thus, any process or thread running Oracle code can safely assume its node or instance is an active member of the system.

If there is a failure, recovery is transparent to user applications. CM automatically reconfigures the system to isolate the failed node and instance and notify Integrated Distributed Lock Manager of the status. Integrated Distributed Lock Manager subsequently recovers any of the locks from the failed node or instance. Oracle Parallel Server can then recover the database to a valid state.

The Integrated Distributed Lock Manager relies on the Cluster Manager for timely and correct information. If the Integrated Distributed Lock Manager cannot get the information it needs, it will shut down the instance.

CM performs the following two types of operations:

Node Monitoring

Cluster Management

The description of these operations is based on Oracle's implementation of the Operating System Dependent layer. Your vendor's implementation may differ.

Node Monitoring
CM manages access to shared disks and monitors the status of various cluster resources, including nodes, networks and instances.

Node monitoring:

Provides the basic node management interface modules needed by Oracle Parallel Server in a cluster environment.

Allows the Oracle Parallel Server environment to discover and track the membership state of nodes by providing a common view of cluster membership across the cluster.

Runs on all nodes and monitors the topology of the cluster by querying all nodes for their current membership.

Detects changes in the state of active nodes signaling those events, diagnosing the changes, and coordinating a new common and consistent state among all nodes.

Notifies Oracle Parallel Server of the actual changes to membership.

Cluster Management

CM determines what groups are up and manages instance members. Each instance registers with its database specific group. This CM function was performed by the Group Membership Service (GMS) prior to this release.

:-() quiet a lengthy piece sorry i thought this might help you.
i am leaving for the weekend .so heres wishing you all the best fort your installation.