Mike,
The difference between RZ and RB lenses is RB lenses have shutter speed control on the lens, whereas RZ lenses are controlled from the actual RZ body. This is not the only difference, but is the most relative to the situation you are speaking of.
Since there is no shutter speed control on an RZ67 lens, and no shutter speed control on an RB body, there would be no way to change the shutter speed of an RZ lens on an RB body. Because of this, I would say they are only interchangable in the direction you speak of, not vice versa.
Hope this helps.
Josh