I think the default styles don't match your requirement, in fact for areastyle it call the GDI+ API:
and all the styles inclued in System.Drawing.Drawing2D.HatchStyle.
So this is the nearest one style I think:
AreaStyle StyleA = AreaStyles.CreateHatchStyle(GeoHatchStyle.WideUpwardDiagonal, GeoColor.StandardColors.Transparent, GeoColor.FromArgb(150, GeoColor.StandardColors.Red), GeoColor.StandardColors.Transparent, 1, LineDashStyle.Solid, 0, 0);
But it cannot set the distance between lines, so if you found a way to adjust the distance of lines of HatchStyle, I think we can try to apply it to our area style.
Here is all the default styles: