Round Edges is working in the scene - the material however is mostly Diffuse, where the difference is barely noticeable, which would be expected. Rounding the edges is most prominently visible on reflective surfaces, as those catch highlights, so the result in your scene as set up is as expected; it's working, but with a material like that, you wouldn't see a lot of difference (same with if the geometry was actually chamfered)
I adjusted the material to have high reflectance just so you can see it is working as expected; rounding of edges, either via shader or via geometry, won't show up a lot on diffuse materials. The images are round edges off, round edges on, and the material set up used; no changes were made to the Round Edges map itself, so it is doing the same rounding with your material, just that with it being almost pure diffuse, the difference is (as expected) not very visible.
Hope this helps!
