Yeah, he describes what I was saying there.
Rewire allows him to sync protools time line with waves tune time line.
It's handy but unnecessary, and completely unrelated to an audio issues you're having, to the best of my knowledge.
Rewire does have other audio routing applications in other circumstances.
For example, you can use rewire to have a standalone instance of Reason operate just like it was a plugin inside of another DAW, like Protools.
It allows audio to be sent to, processed by, and returned from, that standalone suite, but none of this relates to your Waves Tune set up.
If you had issues bouncing your tuned audio before, I strongly suspect it's a limitation of the vegas suite you were using, as I know first hand that Protools and Reaper work straight-up with Waves Tune just as they would with an eq, compressor, or reverb.