"a dim shadow" is correct and usable in written English.
You can use it when referencing something that is faint or barely visible. For example: I could barely make out the shape of a dim shadow in the corner of the room.
Julian motioned to Obie's neck, where Dr. Setumahaven's laser had reduced the spider to a dim blue shadow.
Zyla observes in his book that the difference between persimmon and scarlet can be the difference between a woman's "looking like her full self" and being reduced to "some dim shadow".
In the dim shadow of the canopy her luminous eyes shone more brilliantly than usual, filled as they were with tears of joy.
Somehow, though, I think he would still like to design a garden studded with modern pavilions that would complement (he is not interested in rivalling or bettering) the place that has so inspired him, the Taoist Lion Grove Garden in Suzhou, with its poetically named buildings: the Standing-in-the-Snow Hall, Faint Fragrance Dim Shadow Tower and True Delight Pavilion.
A man stepped out of the dim shadows.
The multitude live in a dark cave and see only dim shadows.
"Across the vast pale desert, haunted by dim shadows of conquests past, rides the lonely hero," we read of L. P. The conquests past are sexual and cinematic -- pornography being high art in Cinecity -- and L. P. is lonely because that is human fate.
Most have been relegated to the dust-bin of history, or only dim shadows of them remain.
The novel tours the new Berlin, from Kreuzberg to the Ku'damm to the American-style glitter of Potsdamer Platz, in whose shadow Dix frequents a dim cafe for schnitzel; we visit the sleazy district around the zoo, where avid East Germans, Dix learns, poured into the sex shops once the wall fell.
It was dark, out on the narrow lane that ran past the sawmills, dark and very green, the boundary wall a dim colony of moss and ferns, the shadows under the trees damp and still.
