Dear Doolarie
Yes, different types of pronounciation do give away from which part of Greece the person that's talking is.

In most cases the pronounciation changes with each geographical territory. In Northern Greece(Macedonia,Hepyrous,Thrace) the language sounds heavier and a lot of times very different than the common(book) pronounciation is.
As we move southern it starts to lighten up a bit, then when you go to the Ionian islands it has more of a singing style into it and the letter E-is very common infront of most words, in Crete we have strong S and R and in Pelloponese they enphasise with N, other "idiomas" like those exist also in the Aegean island and in Cyprus. Of course the language remains the same so if you know it you wouldn't have any problem understanding it.

I think the same happens everywere in the world, when we learn a language we do it by the "book" but in real life its always different.

I hope my post clarified this a bit for you.
don't hesitate to ask more questions