I only have an expired trial of OF but it does let me post a task from the Share menu in DEVONthink. However, for it is using the file URL, i.e., the file path from the Finder. That isn’t a good idea – either in this context or in almost every other I can think of – as the path could change.
However, the script we provide should make a proper task with an item link.
Also, commands in the Share menu are context-sensitive. This avoids displaying menus overloaded with unrelated commands. As OF doesn’t appear in the Share menu for Preview, that’s a question they would have to answer.