Whew!A little misunderstanding, I used anti gel in the diesel fuel tanks, not DEF tank. I just stated that I was more concerned with DEF freezing in winter than diesel fuel gelling.
DEF freezing seemed like a concern when the truck engine is not running for the DEF heater to do its job.
The trucks I work on, at least, will allow sufficient time for the Def to thaw before attemting to inject it. Up to 90 min, from what I understand. Coolant runs through a loop in the tank, through a heatsink in the pump, and around the injector. The def lines and hoses are wrapped together in split loom and some sort of tough tape. In the latest models, the def hoses themselves have a heater grid surrounding the hose and are heated electrically.
My first concern would be to make sure the def system software is up to date. On the trucks I work on, there were initally some problems with codes setting too quickly. Software changes allowed sufficient thaw time, avoiding problems when codes set.
DEF will freeze, and that's ok. The truck is programmed to allow this. Id start it up, do your normal cold start/warmup procedure, and start driving. I could see something like a stuck open/missing thermostat causing the def to stay frozen too long, but that's about it.