The first way (i know) to really combine an other raster (e. g. aerial photo) with RM shaded relief, is over a GIS application. The imported shaded relief (png-file) is not georefereced, this required a spatial adjustment. Export for the IMC processing as geotiff.
I would recommend an shaded relief export with spatial relation in RM v2.
(The lake and the land-area in the picture is not deep/structured, the shaded relief not so clearly visible - it's only an illustration in principle)
The better second way is to use a kmz/kml-file from the RM-export: "google earth map with colour band shaded relief". The advantage is - the kmz/kml is yet georeferenced.
.