Not in Automator. There are other ways but the question is once you have the files what do you plan to rename them. You can't just cut off all the chars above 256 as this will not ensure uniqueness.
So what convention will you use to make the names unique?
As for getting the files. This command run in the terminal will return all filenames over N long
ls | awk 'length ($0) > N'
so in your case
ls | awk 'length ($0) > 255'
So this could be run from an Automator workflow or Applescript to capture the filenames you want to change. But again it's the renaming that is tricky.