From looking at chapter 190, my guess would be that the Vizards are against Aizen, but also that Soul Society doesn't accept them at all.
Maybe they'll fight against Aizen to get Ichigo to side with them, or to change the shinigamis' opinion of them?
But from the way things are going so far, the Vizards probably won't even be needed...
Unless that Arrancar's released zanpakutou is really good, that is. Mind you, Yumichika isn't even fighting yet.