Currently it is not possible to show alerts in alert list with viewer role in a dashboard.
I checked the new Alert List plugin with grafana 5.0 beta. In Grafana 4.6.3 an anonymous user with viewer role could access the alertings from menu.
I create a issue for that, but it was closed because the editor role is needed. I think this is a broken feature. Editing alerts should need editor roles, but viewing them should be allowed for viewer role also. The graph plugin already shows that an alert happens but.