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.
If you drive your robot back, then suddenly forward to get it to tip back,
can you drive forward and slew sideways enough to land on a sack?
haha
foam mats may be ±1" 
At a tournament that we went to for gateway, there was a field where a lot of competitive matches went down and there was a lot of pushing. The field tiles got a lot of gashes and niks.
In designing possible drive bases one of our items was the concern of getting hung up on the tiles where the plate to support the trough is under the tiles.
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.
We haven’t tried that. I think our new robot’s COG is too low to be tippy enough.
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