I want the ability to search for directories instead of filenames.
Much like the File List, the Search Results work on a per-file basis.
In short, Defraggler "doesn't care" about folders, it cares about individual files, so it doesn't really have a way of looking for or displaying folders like you're talking about.
What you can do, however, would be to right-click on a file in the File List or Search Results > Highlight Folder > select the desired folder. This will highlight all of the fragmented files in that folder; you can then check the checkbox for any of the highlighted files to check all of those files if you like.
I'll be happy to bring this to the attention of our development team, I'm just not sure if this would be feasible to add in the foreseeable future, so I wanted to let you know an alternate way to perform this task.