Regardless, I'm not sure if a value of 0 actually does anything that a value of 1 doesn't do.
The way the heuristic works, if it hits any value above 1, which is the expected best value, it will check nearby tiles to see if they are a 1, and path for that, instead, if they are. If you have a weight of 1, which is normally only high-traffic, you just check directly in a path towards the target. In practice, this tends to mean two extra "failed check" tiles on either side of your path with a weight of 2 on "normal traffic". Assuming fairly straightforward pathing, you have 2/3rds of the pathfind filled with unneccessary checks. (In practice, fortress design tends to flood-fill multiple hallways and dead-end rooms unless you explicitly low traffic or restricted zone them, so it would be less waste since those dead-end pathfinds don't have that wasted 2/3rds.)
What A* should look like is
this image, unless Toady has a weird implementation. If there's a wall the dwarf has to go around, it doesn't creep along the side of the wall, it fills every tile leading up to the edge of that wall.
Because of that, a 0 should just make the heuristic behave oddly, and possibly make restricted traffic zones useless. It's probably better to just take the time out to use the system as it was intended, and paint all your hallways and stairs as "high traffic", while painting your rooms and dead ends as "low traffic".