Instead of installing the Zabbix agent, can you configure Zabbix to do
snmp polling?
SNMP can be enabled on the appliances.
Upgrading to SecureSphere v14.2 will disable snmp, and v14.2 has a different way to configure SNMP.
It's in a knowledge base article -
SNMP--Do Imperva On-Premises appliances support SNMPv3