After executing DBMS_SERVICE.START_SERVICE, the service resource remains in an OFFLINE status when I display the cluster resource status. Is that expected behaviour ?
YES this is expected behaviour. Unfortunately, the DBMS_SERVICE.START_SERVICE does not update the clusterware until 11g Release 2. You should use srvctl start service -d dbname then you should see it come online. Note: With Oracle RAC 11g Release 2, the cluster resource for a Service, contains the values for all the attributes of a service. Oracle Clusterware will update the database with its values when it starts a service. In order to save modifications across restarts, all service modifications should be made with srvctl (or Oracle Enterprise Manager).