Can confirm this. I bought a Garmin DriveSmart 65 and loaded an off road Map for snowmobile trails.
It displays the Off road Trails just fine and is a good reference to show you were you are.
However if you are trying to use the Drivesmart to Navigate to a specific destination, it will not calculate a route using the off road trails. You can select "Navigate off road" and it will create a Straight line from your current position to your designation, so its not totally useless....but it can be clunky.
I bought this unit not knowing the lack of off-road capability, so BUYER BEWARE, lol.
Check out the Garmin Zumo XT2 if you have the $$$$
Unless someone has figured out how to put the Garmin Zumo XT software on a Drivesmart, than I may be upgrading....The $600+ price tag is still a deterrent though.