The "Digital Split Image" focus assist (as implemented on fuji's cameras) requires a display, so in pure OVF it is not possible to use it. However, on the x-pro2 you can also add a little display in the lower right corner of the viewfinder: set it to "ERF mode" : http://fujifilm-dsc.com/en/manual/x-pro2/first_step/monitor/index.html#viewfinder_selector
You should then be able to have the split image on the little EVF, with the rest of the viewfinder still in optical.