Is this possible? Can I make some objects not antialias?
Only if you write the antialias all yourself through a shader (FXAA on the board), have all objects that are meant to be AAed on a layer drawn by the first camera that draws which uses FXAA and then draw the non-aliased on top of it with a second camera with FXAA.
if you rely on hardware AA then the whole environment is being AAed, without any relationship to unity and the layers at all
Since Deferred Rendering does not AA and Forward does, you can do it with two cameras with different Rendering Path set. Be prepared for odd depth-buffer behaviour though. And don’t expect it to have better performance than just AA everything.