Passive vs Active comes down to this.
Are you accessing the data for any purpose then NOT passive.
Are you using the "Passive" for reporting then NOT passive.
Are you log shipping as part of your HA HR HP then NOT passive. This is because you canstill access the server and the data.
Is the server the Target server for Mirroring the IS Passive. you can't access the server until failover.
Is the server used to stage data, replication, Data pump to other servers then NOT passive.
Clustering and Mirroring are different and each server in a Cluster needs to be licenced, where only Principal Mirror SQL servers need to be licensed. You can use SQLExpress as the witness therefore no license required. BTW the 90 day moving of licenses restriction applies only to those not purchasing under software assurance and Standard edition. Not restriction, as yet, for Enterprise and SA software.
Hope that helps.