It depends on what is modified in any given mod. Some things that people say are "visual" are actually part of the simulation (e.g the meshes). We only checksum those that are neccessary and ignore everything else. So if the mod is truely only "visual" you should be able to play with someone else using unmodified Sins.
LEt me get this right as SINS currently is at the moment you can play with a Modified visuals only mod with reguler sins players?.
If that is correct would it be possible to get a list fo the folders that contain the visuals that do not modify the simulation and there for would not cause problems witht he checksum. If you can tell me that ill start stiping out everything that prevents me form playing onlien on those visual mods.
Maybe new pure visuals mods will also come out.