Er...if you have the source code and lots of free time, I don't see why not.
But I mean, it's not like you can just drop it onto MagicalUpdater.app and have it suddenly be a saver. OS 9 screensavers and OS X screensavers have essentially nothing in common. In OS 9, they were usually extensions or control panels from third parties and weren't even generally compatible with other screensaver programs. In OS X, they're plugins to the Apple-provided ScreenSaverEngine application.