I have 3 or 4 observations to throw out. First, there are two drawbacks to running a Heisler in snow that I personally observed. First is that the gear cases hang low enough to drag on crossings that are built up with ice and snow. This could result in a broken gear case. The other drawback I saw in my one snow experience was what happens if you start experiencing some wheel slips. It rattles the gears and U joints something terrible. I think it would be a good way to take out a gear tooth.
I suspect that wedge plows work better at speed in order to throw the snow off to the side a little further than if the snow is just pushed far enough to allow the plow to advance. Wedge plows at speed can be seen in a few Youtube videos. A Heisler would likely be better than a Shay for this since the speed can be a bit faster, if those were the only choices. Mark Yates that used to be with C&TS told me that plow service is real hard on crown brasses since they are or were lubed by cakes of hard grease. He said that at the low speeds the brasses and journals don't get hot enough for the grease to melt and do it's job. I guess a rod locomotive with oil cellars and pads would not have this issue.