Yes, it will suck all of the cooling heat out of the cooling loop.
28,000 btu/hr is about 11 hp. The engine that drives that genset is about 10-15 hp. Typically 1/3 of the input fuel is converted to hp, 1/3 to heat in the cooling system, and 1/3 goes out the exhaust. So the hp output roughly equals the coolant load.
Virtually all of the cooling load in the glycol loop will be sucked out by the Heater Craft Heater. And that assumes that the genset is putting out its maximum KW. If the genset is only running at say 5 hp (to supply a 2 KW load) then ALL of the coolant load will go to the heater and the engine will never warm up.
It will be like running down the highway on a cold day in your car with the thermostat stuck wide open.
A 10,000 BTU heater might be ok, but not the 28,000 BTU one.
David