Different retention policies for datafiles and archived logs

No, the retention policy applies to both, rman datafile and archivelog backups. But you can define an archivelog deletion policy that applies when deleting archivelogs. The policy by default it is set to none. Please see the documentation:

https://docs.oracle.com/cd/B28359_01/backup.111/b28270/rcmconfb.htm#BRADV89439

Keep in mind that RMAN does not delete anything unless you instruct it to do so. If you configure FRA, and there is space pressure, only then will Oracle automatically delete files according to your retention and archivelog policy. The policy also applies when you backup files using "delete input". Also, no rman backups are considered obsolete regardless of age, when the data is required to fulfill your retention policy, e.g. older parent level 0 backups.