The D&RGW regularly used dozers as part of their snow fighting equipment. They continued to use the Rotaries, Spreaders, and Flangers as needed when major snow events dictated their use. It was pretty easy for the Rotary to plow deep fresh snow and would be much more efficient than a dozer. The use of dozers in the Animas Canyon was for practical reasons due to all the rocks and other debris found in the slides which would regularly block the line in winter, the Rotaries could not be effectively used in the Black or Animas Canyon's for this reason. The other common tool used on the Silverton branch and over Cumbres were the large wedge plows mounted on a locomotive. Remember that snow removal during the D&RGW days was removing fresh snow. I believe Jimmy Blouch posted some photos of the train opening the line in May of 1965 after the first winter of no train operations over Cumbres and it shows a dozer being used on what was undoubtedly hard crusted snow at that point. Hope this helps with some of your questions.
Thanks.
William
aka drgwk37