Welcome to the Community - If you are referring to the ESXi Software iSCSI Adapater it will actually use both the Storage stack and Network stack - the storage stack to maange the storage and the traffic will be carried by the network stack -

By default a vmkernel is created when you intsall ESXi - so unless you created a new vmkernel port used specifically for iSCSI your iSCSI traffic is sharing the management port -