It's been very hard to get ANY information on this VST(?). So if I read you right, you lay down the vocal track in Vocaloid, then export a wave file which you import into Mixcraft, kind of like Beatcraft for a voice?
Yes, seems like it isn't very common. Apparently it's a hit in Japan (you can choose Chinese, Korean, Japanese and English as the program language), but it's not really a music program or an actual plugin. Bestservice had it in their catalogue, but it was misleading, since it is called a VST plugin, which it isn't.
It's a vocal synthesizer - you can type words and notes and a female voice sings your lyrics in the key and tempo you decide.
Seems like you can import a mp3 or wav track (maybe if you wrote a song in mixcraft), then you can create the vocal track in vocaloid and export it, and re-import into mixcraft. I'm not yet certain about all the features and how it works; it's not very user friendly, but it produces nice results, judged by the examples from the web.