It looks like Ray operator is watching only a namespace that it is installed in - I installed it in the namespace Ray and now can create clusters in this namespace. But if I try to create a cluster in the different namespace, I see RayCluster object there, but the cluster is never created.
The operator is currently namespace-scoped. Thus, for a RayCluster resource to be processed, an instance of the operator must be running in the same namespace.
Adding support for running the Ray Operator as a cluster-scoped controller is an open action item
See also this post