put that z depth map into blender and use it to create a bas-relief of the scene
Do you mean use Z depth information to create the landscape? What is the form of Z depth information? Blender can use grayscale image to create Z depth using Displacement modifier:
You can easily discover z -depth values you would need to map to [0-1] using camera limits visualization and clipping values.
Set clipping value sliders so that limit line starts and ends where you want to. Closer you adjust more depth resolution you will get.
File format - Openexr will have most of the details, png 8 bit will capture least amount and will show banding likely. jpg hopelessly distorts what you would render.
Do not relay on your eyes when looking at greyscale image - use mouse rightclick and drag cursor over the image in UV editor window - values will read on status line. http://www.pasteall.org/pic/show.php?id=92838