Checking the archive and archive_command is primarily for Point-In-Time-Recovery. If you want to monitor a streaming-based setup, it is advised to keep an eye on a system view called pg_stat_replication. This view contains the following information:
test=# \d pg_stat_replication
View "pg_catalog.pg_stat_replication"
Column | Type | Modifiers
------------------+--------------------------+-----------
pid | integer |
usesysid | oid |
usename | name |
application_name | text |
client_addr | inet |
client_hostname | text |
client_port | integer |
backend_start | timestamp with time zone |
backend_xmin | xid |
state | text |
sent_location | pg_lsn |
...