Roles are excluded from the capacity amount in the Project & Portfolio Management (PPM) Capacity Overview Portlet, but they are included in the Allocations. It appears Capacity only populates for named resources with the role assigned.
This is working as currently designed as Capacity is based on the amount of time resources are available to work. (See the CA PPM Glossary for more details on Capacity)
The one option to workaround this to include role in capacity calculations would be to create placeholder resources to use in calculations versus roles.
For documentation on this portlet reference Capacity Overview Portlet