A suggestion.
You could use the Copy URL feature in Yummy for the login directory of each of your servers, and if you have the 'Export passwords in urls' option checked in the Server Options panel of the Preferences then a fully qualified URL will be created which should be enough for any FTP client to import.
Of course you would need to do this for every Bookmark you wanted to export, and then paste the results into a text file (etc), so it's going to be a problem for a lot of Bookmarks, but it could be a viable solution for you.
Hope that helps...
