But the study's already been repeated all over the world in prisons, so it's reproducible.
In other words, are the guards behaving like jerks because their power has corrupted them, or because behaving nicely is likelier to lead to them getting attacked by prisoners?
Another consideration is that while I'm sure abuse in prisons is rampant hopefully it's still far from the majority of guards behaving poorly. If that's true, then real life prisons might be evidence against this conclusion as most (hopefully) prison guards wouldn't be jerks.
I suppose we could look at jails, then. They'd mostly be full of people still presumed innocent, and most of those who are guilty aren't guilty of a violent offense. If you just wait a while, you can find out which of those presumed innocent people people were found not guilty. It'd be interesting to see how the guards treated those people.
Abu Ghraib doesn't boil down to uniform and a prison setting. The perpetrators believed themselves to be in the right and Iraqis to be deserving of punishment before they were ever placed in the prison setting. It doesn't map onto the SPE at all, despite countless commentators drawing comparisons between the two when the Abu Ghraib story broke.