Rear filtration is a fringe benefit of the Z system, made possible by the very short register distance (16mm). This is useful in particular for UV where the filter options are thin on the ground and tend to be very expensive for larger sizes, if they even exist (often, not at all). Besides, the very efficient Baader U filter is dichroic and that spells problems with a wide-angle lens. In such case, for an optical design with a small exit pupil like the OM 28, rear filtration is much better.
The filter box can be replaced with an ordinary FTZ adapter if "normal" visible light photography is intended. Then, as the OM 28 lens is "chipped", all lens information can be seen and recorded in EXIF. The OM 28 does UV, but only the upper UV(A) band. Suffices for floral studies and landscapes at least.