According to the Post Gazette's article Pirates Notebook: Van Benschoten might have upper hand JVB has the upper hand amongst the AAA rotation. The article highlights all the pitchers who could be in the mix including relievers if Chacon gets the call.
Cota gives insight on each pitcher, since he just got done handling them during his rehab.
Chacon has hinted he has already been told he will not be the 5th starter.
If Tracy is waiting until Tuesday to make the call, JVB is pitching Tuesday for Indy, then I would have to say the call is already made. The roster move won't happen until after Indy's game is done or JVB finishes his outing.