The initial press release announcing the tour claimed that former Zappa collaborators such as Vai, Adrian Belew (who has since confirmed that he is not, in fact, participating in the tour) and Ian Underwood had "committed" to the tour.
Vai wrote that while the endeavor struck him initially as "odd," he added that he soon began to feel that it "could also be pretty special too."
"A day doesn’t pass that I don’t think about Frank. Nothing could, or ever will take his place in the hearts of the fans, his family and the musicians that have toured with him and loved him," he wrote.
"I believe that the fans understand it’s just an image and that holographic technology has its limitations, but it is an evolution in technology and with an open mind it could be embraced for a worthwhile experience," he added. "I would want to attend this show if I heard about it. If a person can attend the show with their spirit of the love of Frank’s music at the forefront I believe it could be a very touching event for all involved."
Vai said that he will contribute to "3-4 shows" as part of the tour. Over the weekend, Zappa's son, Dweezil—who for years has played his father's music as a part of his Zappa Plays Zappa tours and was also mentioned as a possible participant in the hologram tour press release—confirmed that he would not be involved.
You can read Vai's full statement on the matter here.