The SNMP OIDs used by the interface_traffic probe actually contain the total bytes for each interface, not the per-second average. (They are knowns as ifInOctets and ifOutOctets.) The interface_traffic probe just does the math for you automatically. If you want the raw values, the easiest way to retrieve them would be the snmpget probe. And you can configure a threshold in the probe for those OIDs to generate an alarm on the total in or out bytes transferred.