I tried creating a character with textured eyes, and those faces that use the eye textures are completely separated from the body, but the faces of the eyes are right very near to the body so there won’t be any small spaces visible.
I also wanted to add a subdivision surface modifier so the character would look smooth in the rendered scene, the problem here is that the smooth normal don’t work with that modifier. As long as I use the subsurface modifier on both body and eyes, even if they still look completely attached, the normals won’t cooperate with the modifier.
this is a bug present in both 2.79 and older, and 2.80 beta.
Applying the modifier won’t fix the problem
Or I might not know what else do I need to do in order to get the smooth normals in subdivision modifier