Are the metrics for Email Templates across all Campaigns?

Yes. The metrics shown on the Templates tab are the metrics against all campaigns for that particular template since email template can be used in multiple campaigns.

The break-up of metrics for each campaign using the template can be viewed by visiting the detail page of the template.�Click on the name of the template on the Templates tab. You will be redirected to the detail page of the template. The metrics for each campaign using the particular template will be displayed.