While reading the OpsCenter 5.1 docs, it looks like OpsCenter can’t work if Cassandra does not provide a Thrift interface (see  below).
Is it really the case ?
At first sight, it sounded weird to me, as CQL 3 is provided for months.
Just to know, is a OpsCenter future version, not relying on a mandatory Thrift interface, on the road ?
 in the OpsCenter 5.1 guide :
*** Modifying how OpsCenter connects to clusters
Cluster Connection settings define how OpsCenter connects to a cluster.
About this task
The Connection settings for a cluster define how OpsCenter connects to the cluster. For example, if you’ve enabled authentication or encryption on a cluster, you’ll need to specify that information.
1. Select the cluster you want to edit from the Cluster menu.
2. Click Settings > Cluster Connections.
The Edit Cluster dialog appears.
3. Change the IP addresses of cluster nodes.
4. Change JMX and Thrift listen port numbers.
5. Edit the user credentials if the JMX or Thrift ports require authentication.