nearly everything *can* be mounted on a 4/3 or NEX. The only thing that would prevent a lens from fitting onto a camera is if it's flange distance is too long. Because you can always add distance, having a few millimeters from the flange to the sensor permits virtually any lens to fit, provided that you have an adapter available.
If the flange distance is too long you can still focus at close range, provided that the working distance is greater than zero, however, you will not be able to focus at some distance and never at infinity. Effectively the camera would become an extension tube in this configuration.
But yes, because all film cameras I can think of had flange distances far more than NEX or 4/3, you will be able to use just about any lens. It's just a matter of having an adapter.