Even with the same beat it doesn't necessarily work. I used a on-vocal and off-vocal of the same song and it didn't work as well as i thought. Though...I have to admit that the songs may have been at different timings (Maybe...a few ms apart?) and that might of impacted it.
Ahh that's good to hear. If you need someone to help or check the final product, just ask me. Since i've got a lot of free time at the moment.