Yes, it would be a great source of coolant flow for a choke. You will want to find a similar one for the other end, one should be a "supply" and the other the "return", meaning near the inlet and outlet to the water pump. Usually you can look at the 5/8" hoses to the heater core to help figure this out. The heater core and choke hoses are not thermostatically controlled and so are first (after the engine itself) to get coolant heat.
If you want to cap it use a rubber cap sold for the purpose and clamp it. There may also be an outlet available without the smaller nipple.