I think that it would work well as long as it isn’t putting friction on the ground, worst case scenario is that somehow a sack is so flat to the ground on one side that it somehow slips under, but the odds of that are slim to none. It would depend on how well the field re-setters do.
Both using a skirt/low-chassis or a tank drive for climbing over the sacks are good ideas, but I personally like the low chassis, because I would spend more time picking them up than running them over.
Our protective skirt has more ground clearance. It’s between 1/8" and 1/4" off the ground, and we tested pushing many different orientations of sacks; flattened sacks, plump sacks, neatly placed sacks, carelessly dropped sacks. None of them penetrated our drivetrain.
You do need to remember that not all tournaments place fields perfectly flat on a perfectly level floor. With ground clearance as small as 1/8" (3mm) you run the risk of getting hung up on fields that are not perfectly level. The low-clearance model is certainly viable, but remember that no one promised you perfect fields.
I heard that at the math division at worlds that there was a major dip in the field that barely anyone noticed or brought up. I wasn’t in the math division but one of our teams mentioned that they kept getting caught on the field.
When we arrive at a tournament, several of our members go out to inspect the fields. We make sure that all of the goals are bolted, and that all of the tiles are flat enough. If they are not, we kindly ask a volunteer to address the issue (or ask permission to help address it ourselves). Our habit of field inspection began after this happened: http://www.youtube.com/watch?v=-rIsHrTSqqw