Hi,
I think Yes, the supply to the heater core typically comes from the rear of the block. If you remove that hose at the heater core connection, it should pump out coolant when you rotate the engine with the starter, indicating the water pump is working. If you are not getting any flow you might have a blockage. Blowing through the hose should allow air to pass. For proper circulation coolant needs to flow through the rear hose and return from the core, even if the heater is off. Ensure there's no blockage in the cooling system.
Thanks