The problem is that OkMap isn't able to import osm file. The only vectorial data that OkMap can import are: Esri shape file and Digital chart of world. Check if there is a tool to convert osm to shape file and then you can import into OkMap.
I was trying to find out also if OkMap would work with OpenStreetMap data.
I've recently begun using OkMap as a tool for working with my Garmin GPS tracks as a step in their use for adding map data to OpenStreetMap. It's a very useful tool - and I'm please to find I can easily download rendered OpenStreetMap images, and it integrates well with my custom maps...
I've been thinking about adding a little more information about OkMap to the OpenStreetMap wiki... but I was thinking that lots of people would only want to use it if it integrated with OpenStreetMap a little better. Is this something you might improve? Would it be possible to provide an OSM background image? Or would it be possible to import OSM vector data? I don't understand what's required for this development, but it feels to me that this is not a very difficult development? I think that there is only one step missing somewhere.
Have you consider to convert OSM vector data to ESRI shape file format? Which are the information that will be lost in the conversion? I say that because OkMap now manages only shape file information stored in the shp file, so it's important to know which information I'll add.
Consider that OkMap borns to manage raster maps. Vectorial maps are an add-on often useful to integrate raster map with own drawing. I think that, to make OkMap able to render OSM vectorial maps, is required a lot of work.