AppInsight for SQL, included in SAM 6.0 (Currently in Release Candidate) includes native monitoring of database mirror status. (sign-up here)
AppInsight for SQL also includes visibility into the SQL cluster members and their status when all cluster members are added/monitored by by SAM. Below may be a poor example, as only the cluster VIP is being monitored by SAM, but if the physical cluster members were also monitored their status would be shown next to the node name.
