That would be nice feature to have. That will make things so easy. In a large environment, I don't want to add the resources manually in vCOPS. Once, the tag is defined, hopefully when ever we add more resources to vCenter server, vCOPS/custom dashboard gets updated automatically.
I run enterprise version, and on env overview page, left hand side widget has manage tag resources. Use that to add a tag group. then add a tag value... I did one for storage arrays. I had to add a tag value for the many array groups... example emc2012. Then I drag and drop the datastores into the tag group and it updates when new tags matching that criteria are discovered.
My app groups dont, which is a possible enhancement because its a time drag to have to manage app tiers manually. Maybe 5.6 and something like navigator can address this, but who knows.
Hope that answers the question.