(Salut, je te réponds en anglais ci-dessous car c’est la langue de ce forum)
I have never had this problem before.
I’d suggest you use V-Ray materials only. You might get confused otherwise. Also, double check that your Rhino objects don’t have materials specified “by object” which might override V-Ray settings.
As a last resort, invert your opacity texture in Photoshop and reload it.
Representation of V-Ray materials in Rhino viewport is approximate. It is not possible to guarantee that for every option you have in the Asset Editor will yield a correct material in the viewport. In fact for most of the option - it will not.