I have seen comment about not allowing spaces in path to gs in new PDF annotate feedback plugin. This can easily be avoided adding a string
$gsexec = escapeshellarg($gsexec);
before adding $gsexec to the $command. (We have similar problems running dot utility)
Also, all other paths in Moodle used to be defined in Server/System Paths even if path is used by one simple plugin, I see no reason to add gspath to other place.
Hope this will help authors of plugin to make it better.