if min < Density < max will the polygon generation still generate polygons for that density and the voxels behind it?

I havn't dug too deeply into polygon generation and I'm thinking I can do transparent (Not alpha blended) voxels with this method.

I'm not sure I undestand your question. The min and max values of a voxel are defined by the data type, e.g. for Density8 they are 0 and 255. The density value of a voxel must always be between these (the relationship you specify is always true). The threshold which is used for marching cubes must also be between these, and by default it is halfway between them.