Here is a folder action that does not depend on third-party actions for directory comparisons. Tested with Python 2.7.10 on OS X 10.11.5.
Files in Folder A:
Files in Folder B:
The first action, Ask for Finder items assumes that you are going to select the first folder, and then press the command key, and select the second folder.
These folders will then be passed onto the do shell script action as arguments, and pulled off the command line in order right into dirpath1 and dirpath2 variables in Python. The standard Python filecmp module uses its dircmp to recursively compare each directory (and sub-directory if it exists) contents. Finally the report_full_closure() method writes out the results that are passed on to the new text file action.
For the above two folders, the report in the text file is as follows. The None indicates it found no sub-folders. Save the workflow below as a Automator Application.
diff /Users/viking/Desktop/A /Users/viking/Desktop/B
Only in /Users/viking/Desktop/A : ['test.pages']
Only in /Users/viking/Desktop/B : ['date.pages']
Identical files : ['hbo.html']
None