Backups done with Barman on PostgreSQL servers that were created with initdb --xlogdir, lose this link when they are restored. Could the location of the xlog/wal be captured during the backup, and then when the restore is done put that link back in place?
I have split my xlogs onto a different filesystem, and not having the link means I have a few extra manual steps to do after any recovery.
cd $PGDATA/pg_xlog
mv * /var/lib/pgsql/9.6/pg_xlog
cd $PGDATA
rmdir pg_xlog
ln -s /var/lib/pgsql/9.6/pg_xlog pg_xlog