Folders on top, on desktop
You can sort your Desktop as you can do it with your Finder folder structure.


  Just sort by "Tags" and thats it:




In my tests, folders are showen before other files. 
But of course, if you have Tags given, it gets sorted differently.

So three solutions:


Give specific Tags and sort by Tags
Give non Tags and sort by Tags
Give your folder names starting with "_" or "#" and sorty by Name