Hi,
Try using the cmdlet Add-SmBackupDataset Refer https://library.netapp.com/ecm/ecm_get_file/ECMLP2440057
Refer page 8 Resources: For availability group backup @{"Host"="localhost";"Type"="SQL Availability Group";"Names"="AG1"} Valid Type values are: SQL Database, SQL Instance, SQL Availability Group. You can include comma-separated values for Names.