The message says that Fuji X series cameras are currently not supported.
This is all it says. It's accurate.
As far as I've learnt from several sources, DxO uses it's own algorithm to demosaic the "common" Bayer patterned raw images. DxO's magic does not work with Fuji's proprietary pattern.
Nevertheless, other applications do work with Fuji's pattern. DCRAW for example. From a customer point of view, there seems to be no special hurdle to overcome except maybe DxO's commitment to quality or it's financially oriented approach. A few years ago market leaders were Canon, Nikon, Sony and fourth, Fuji...