Umit,
As a network and security engineer, I completely understand your team's concern. However, WMI is no less insecure than SNMP. Both offer protection against unauthorized access if configured correctly, and both are needed for Orion to pull information from a windows server for the "complete picture." SNMP is good for standard MIB2 data (CPU, Memory, Interfaces, etc.) and WMI is better for application data (DC services, etc.).
D