These "rockstars" usually come in and create massive amounts of work. Destroy pretty much everything and then leave before the cleanup is barely started.
Whereas the true rockstars will simply come in, quietly code for a short while, and solutions are born. Often these are things that other people can then work with making them better as well. If there is horrible work that does have to be done then again the rockstar will quietly nod, find the few in-house good programmers, spend a weekend or two, and then present a working robust replacement for the terrible system. Not something that is "almost done" (as in half baked) but a complete solution with in-house talent that can work with it.
If anything the surest sign of a rockstar is that there will be little or no squabbling. If there is any squabbling with the in-house developers it will be with the resident blowhard who will be heard saying, "That system won't work, we need to stay the course and use the technology that I have 8 certifications in."