I see what you are trying to do now. The Group alerts are meant for the overall status of the group, not for individual members of the group. My suggestion to achieve both your grouping and alerting objectives is to use Custom properties (Settings > Manage Custom Properties).
You can then reference the custom property in the Alerts like shown below
You can create a Group using a dynamic query
So, you just have to manage the assignment of nodes in the custom property editor and it can be carried through for groups and alerting. You can also use this for changing the hierarchy of All Nodes resources, filtering various dashboard resources like the Top xx resources, etc.