In general the answer is yes, a dedicated subscriber is required for call center agents when they reside within a cluster with other standard phone users.
However in some cases this is simply a waste of call processing resources or is not feasibly possible.
I am on the UCM megacluster review board and we have reviewed and approved some exceptions to the policy to put all UCCE agents on a dedicated subscriber under either of the following conditions: 1) The number of agents was so low AND the overall call processing resources were low and hence it was a very safe thing to do to add the agents to existing subscribers. 2) The agents were very distributed and it wasn't practical to force all of them onto a remote subscribers.
In the end, you want to provide stability for your network. Mixing agents with high call rates and availability needs with standard users is rarely a good idea. If possible, you are better off separating them off to their own subscribers. Especially with virtualization on UCS, it doesn't make sense in most cases to mix them.
