I think it has to be local as the blcli-docs describe:
Command Input :
Variable Name Variable Type Description fileDir String Directory containing the CSV file. fileName String Local file in CSV format containing property values. See above for a more complete description.
You could just copy it locally first using NSH and then execute the blcli.
Blcli commands cannot access remote paths, the file should be available locally. You may copy the file to AppServer first and try running the commands.
Not exactly all blcli , addServerToServerGroupByName will work with remote paths