Not sure what you mean by "FLV plug-in", but you don't have to provide your video in FLV format to upload to YouTube. YouTube will transcode the uploaded video for you. You can export in one of the available video formats under "File" => "Export movie" in Movie Edit Pro. YouTube will support a variety of them, e.g. MPEG-1, MPEG-2, DivX (in AVI file) and WMV (Windows Media Video).