You have chosen two perfect poems to compare and contrast! Further, the poetic elements of imagery and theme abound in these two poems.
Both of these poems have incredible images that appeal to almost all of the senses. In "The Snow Man" we have the first half of the poem concentrating on very vivid sight images mixed with touch images, for example "the frost and the boughs" and "the pine-trees crusted with snow" and "the junipers shagged with ice" and "spruces rough in the distant glitter." Near the middle of the poem, Stevens begins to focus on sound imagery with "misery in the sound of the wind" and "the sound of a few leaves." This leaves the poem wide open to suddenly speak about "the listener" which could be the speaker or US, as readers. Further it is this "listener" who "listens in the snow." Therefore we have a combination of sight and sound and touch by the end of the poem. Then there is the irony of the multiple mention of "nothingness" at the end of the poem, almost proving a purposeful LACK of imagery.
In regard to the images in "Desert Places" by Frost, we have more general images used; however, again they are found in the first half of the poem and, again, they are all sight images mixed with touch. For example, "ground almost covered smooth in snow" and "a few weeds and stubble showing last" and "blanker whiteness of benighted snow" and "animals are smothered in their lairs." And here we have, with the word "smothered," the idea that this might not be a totally positive poem about nature. Of course, Frost's ideas leave imagery and delve into the philosophical idea of loneliness.
The theme of both poems is similar: winter leading to the negative emotions of either loneliness, fear, or even nothingness. For Stevens, the end of the poem speaks volumes:
For the listener, who listens in the snow,
And, nothing himself, beholds
Nothing that is not there and the nothing that is.
In short, winter begets nothingness. It is not a positive image. The speaker, or should I say "the listener," is also "nothing himself." Further, "nothing is not there" and "nothing that is."
For Frost, instead of "nothingness," we have another negative emotion: loneliness.
And lonely as it is, that loneliness
Will be more lonely ere it will be less -
A blanker whiteness of benighted snow
With no expression, nothing to express.
They cannot scare me with their empty spaces
Between stars - on stars where no human race is.
I have it in me so much nearer home
To scare myself with my own desert places.
And not only loneliness, but MORE loneliness before the feeling goes away! Note the similar use of the word "nothing" here (like Stevens) when Frost expresses this. In Frost's case, nature now has "nothing to express." Obviously, Frost has enough fear in his own "desert places" of loneliness that he doesn't even have to think about the vastness between stars that the scientists tell us about.
In conclusion, we can say that both Robert Frost and Wallace Stevens stick to their usual subject matter of the natural word in, this time, speaking about winter. Both of them are well known (and highly regarded) for their nature poems.