Well I did some additional testing:

basically shader or not, if I import a mdl7 mesh in the game and I lauch it I see it in transparency/wrong rendering. Therefore to fix it I flag it "overlay".

BUT

If i mantain the overlay flagged on a mesh that has a normal map everything will turn invisible and i won't be able to display anything.

So my guess is, there's something i'm doing wrong when i export the mesh.

Basically from max I export in .ASE. Wrong choice?