Dave,
If you have a Dometic RM1350, the water feed solenoid on the back of the fridge, and a bit of the feed line from solenoid into the fridge, are electrically heated. It's part of the RM1350 build. But I doubt very much that the poly line to the solenoid is heated, unless done after purchase.
Our 2011 Landmark has the poly line teed into the PEX behind the UDC. From there is goes down and emerges from the frame and is routed under the slide and up into the back of the fridge. Your 2012 is probably the same. If you locate your water feed line, you could tell us if it's insulated or heated. Maybe post a picture.
As for Heartland adding heat tape, and a more expensive water feed line that will support heat tape, who knows. But I think if they did, we might end up with just as many posts asking why the trailer battery is dead.