Hi Vaibhav,
As of now grouping metrics is not an option in custom dashboard given that the tier/app level metrics for indivual EMS queues at node level is not available.
However i have suggestion here, as we support wild card in rest api see if you can manipulate rest api data response and report back as custom metric data helps here?
https://docs.appdynamics.com/display/PRO41/Extensions+and+Custom+Metrics
https://www.appdynamics.com/community/exchange/extension/java-sdk-for-controller-rest-api
https://docs.appdynamics.com/display/PRO41/Use+the+AppDynamics+REST+API (Navigate to metric browser and select "copy rest url" on one of the target metric at same metric folder structure and then past the URL in another tab and change common segment or string in rest URL with asterisk and you will response of each queue and you could this response as custom metric)