As I haven't watched the SEs in a very, very long time, I don't know how it sounds in that version. But in the 1977 mono mix (my preferred mix), they're clearly different voices, i.e. one stormtrooper says "Close the blast doors!," then a different one says "Open the blast doors! Open the blast doors!" The second line ("Open") is a somewhat deeper voice than the first line ("Close").

And Tailguy, I agree about Beru's voice. The mono mix dub sounds more natural - the other one sounds too obviously dubbed to me.