S3 and backups

We're using 8.7.1NE and are interested in using S3 storage for HSM. How does HSM on S3 effect backups?

Will we be still be able to use the NE backup software?

What happens when data is stored on S3, will the backup pull data from S3?

The documentation says ZxPowerstore is compatible with S3 Infrequent Access. Won't this become expensive if backups access data regularly?

Thanks