OCS Inventory NG is not a solution for supervision (like Nagios, Zabbix, ...).
The best is to use network connected printer : they have an ip address, so a simple ping give an answer (and if they support SNMP, it's possible to retrieve lot of informations like page count, ...). It's easy with Nagios or Zabbix to get informations.
For USB printer, they depend of the computer and they could appears in printers list even disconnected : maybe asking Windows with scripts ?