I opened for Vai one time. I saw that stuff too. I was pretty let down and disappointed. Really shocking to me that even pros these days are using tracks and charging for it. More surprising than anything else I guess, but Phillip Bynoe is an awesome bass player regardless, and it's pretty hard to be critical of Steve Vai. Bands like the Eagles never did that crap, and they were fantastic. They probably do nowadays, though. Lots of local bands are doing it here, too. I was playing a gig filling in with my buddies band, and we were getting ready to play that wagon wheel song. It has an acoustic guitar intro. My buddy who fronts the band plays acoustic guitar, and actually plays it pretty well. To my dismay I heard the intro, looked over, and he wasnt playing. I hung my head in shame that night. Super embarrassing to me. Fiddle and guitar, with nobody behind the wheel. Luckily, some of the more high profile venues here, though not many of them, wont hire bands that run tracks. Good for me, bad for a lot of bands that have come to rely on them for their performance.
That was the only time I've ever seen him do it- generation axe, new band.
Otherwise he might have a sampler for certain sound effects triggered by ususally whoever the bass player is Phil or Bryan and everything else is 10000% live