It varies between stutterers. It's also likely to vary throughout your life. We might think that there are certain parameters that influence our stutter, and for some, alcohol can affect some of those parameters in a way that makes speech more likely to come out clean. Of course, it'd be more convenient to figure out those parameters, and to work on them without alcohol. I've had it happen in all combinations (stuttering and not stuttering while drunk and while not drunk), so for me there's nothing concrete. Like I said, it'll vary between stutterers (and over time).