It's not quite so easy to get a really good cohesive system when you are integrating half a system from two vendors.
I would certainly pilot it, and would consider evaluating an all-Cisco solution as well. Yes, Jabber doesn't have all the features that Lync has, but it does have some benefits comparatively, especially since you obviosly don't buy into the 'no one needs a real phone' MS point of view.
Bear in mind that Lync (with EV) is a PBX. CUCM is a PBX. You will be configuring two dial plans, two sets of features, and have all the other interop issues that will cause... not to mention the ongoing support costs and complexities.
The 'create a LYnc number based on the CUCM number' you describe is not something that exists as part of either system. Third parties might do soemthing, but most likely you will need to learn to read data from CUCM via AXL, and based on that data generate configuration in Lync via powershell. It is feasible if you have the skills.
Additionally, you cannot have the 'same' number on both systems. You must have distinct numbers so that routing works properly. As I understand it you would achieve simultaneous ringing accross Lync and CUCM using the CUCM mobility/single number reach system - and if you wanted it to appear as the 'same' number you would need some careful number transformations/translation configuration to achieve it.
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