Sorry, missed this thread until now. The answer is NO for the electric versions if the plan is beyond 30 miles and 30 miles per hour maximum speed.
The answer is YES for the 451 and 453 gas versions, following a very specific set of instructions without any exceptions or you run risk of damaging or destroying the transmissions in those vehicles.
My 2012 Passion Coupe weighs a little over 1,800 lbs. A picture of it on the trailer. Lost count of the number of times I would have had to disconnect had it been towed "4 down".I considered that option of trailer towing. I most likely will opt for that. What does the Smart weigh in at?
It's going to require a bit of work on your part but the definitive way is to check the owners manual of the model you're considering. Here is the link to all of them: https://www.smartusa.com/vehicle-manualsHow do I identify the Smart's models that can be towed flat