Here is another data point. My Mahindra 1538 has a fitting inline to the lower radiator hose. It has two ports, one for a heater for the coolant and I'm thinking the other port is for the heater in the cab version. Seems like the factory thought that a heater in the lower rad hose was a good idea.
The 1538 has an intake heater for starting which I don't think works very well. It will start in the upper teens, but lower teens and single digits it is a crap shoot. At the start of this winter I added a generic coolant heater. Haven't really tried it out yet as I've been using the UTV with a Moose plow to clear the 1/4 mile driveway. Tractor with the front blade only comes out when the snow is deep and/or wet. We still have March and April to go so I'm certain the tractor will get some use.