We cannot currently pull relationship or rollup fields into Dashboard reporting. We are using relationships & rollup fields to keep regularly updated fields up to date across all lists/tasks (i.e. if a person's manager changes and they're also on our training waiting list, we only have to change the manager in one place but the info flows through to the linked task in the waiting list as well). For example, I'd like to be able group a dashboard chart by manager to see how many people with the same manager are on the waitlist (or from the same team, in the same level, etc.).