Manfred,
Yes, its absolutely possible to backup directly to a NFS mount shared folder from the SAP Hana Studio. Process would be similar to that of maintaining backup on to a local folder.
Prior to initiating backup ensure that the mount location is active, or execute mount -a command under root user to load all the configured mount points.
Also as a best practice verify the last complete backup status in the backup catalog and ensure it is completed successfully. If you find a running status for long time you need to check the logs and cancel it (CANCEL BACKUP <Backupid>) if required. This may also require a reboot of the Hana instance.
Next would be looking for sufficient free space in the NFS share folder, as quoted in the backup dialog.
Lastly, In the backup dialog, specify the full path of the target location. For example,
\<nfs_mount_name>\HanaBackup\HDBBackupDate
Refer to the below OSS note for known issues with NFS mounts as target locations for backups.
Note 1716418 - Data backup hangs when writing to NFS server
In our experience, we found out that maintaining backups using hdbsql commands is much efficient when compared to backups from SAP Hana Studio. These hdbsql commands can be automated by scheduling jobs in cron tab. Refer to the SAP Hana Administration Guide for details.
We haven't yet tested the recovery scenario, hence cannot comment on it 
Hope the above information regarding the SAP Hana backups helps.
Regards,
Srinivas K.