I had been playing in Open G, but omitting the fifth string, playing like a guitarist on a banjo. Playing more like a banjo player, the G makes sense for the Em and the G, but not necessarily the D.

Also: structuring a banjo part based on what many call the basic strum, it would be necessary to use the G.

I did think through it in G minor tuning and capoing down (meaning it would be an open Em), but playing the major chords becomes very awkward.