Thank you for such a great question/request.
Out of the box you can do Top X dashboard for resouce pools (this way you can scope to group of VMs), or for the selected Host, Cluster, Datastore and some other parent objects. You can select a cluster and open Top X Hosts dashboard or Top X VMs for the selected Cluster.
However this is not the same as scoping our Top dashboards from the Views folder. Or scoping a dashboard to a group of objects. You are absolutely free to copy and re-use our configuration, however I'm afraid with Dashboards this could be cumbersome, they require huge XML code and also could contain some hard-coded things here and there.
There is a way to limit objects in other SCOM views - by creating a user role which can see only objects in a certain group, but this not always work correctly with dashboards as well as with diagram views, because in most cases they are scoped to a certain group, not a class of objects.
Let me check what we can do on our side to help you with such a request. I'll update the topic shortly.