The problem is that the variable is not evaluated - it contains the string '=concat(GROUP)', not the outcome of $(vCycle).
You would have to set the variable every time the selection in GROUP is made. I tried both Document trigger and Field select trigger but they do not work with nprinting.
What you can do is create recipients with filters per Group entry. You can have recipient name in the directory. But that becomes major pain if you have more and / or changing groups. You would have to export groups and then import them as recipients every time as part of running the task.