In NetScaler Configuration > Instances the CPU usage is different from the CPU core usage under Monitoring tab.

The CPU usage column in the NetScaler Instances shows the CPU usage from NetScaler VPX point of view.

CPU Usage under Monitoring tab shows the CPU usage from hypervisor point of view.

NetScaler packet engines spin in a loop continuously to process the packets as soon as they reach the appliance. Because the NetScaler appliance is spinning continuously, its utilization is higher from the hypervisor point of view.