If you can put it over the stain I don't know. Danish Oil is water resistant and doens't affect your spine. It'll make your arrow darker. which looks very nice. You don't need to stain it before. A lot of friends of mine put it directly on the shaft, a few layers.
Danish Oil consists out of a lot of Tung-Oil, which is used for ages in Asia to impreg wood (i.e. ships) to make it water-resistent.
As a matter of fact, I usepure Tung oil to seal my shafts. First layer 50/50 Tung Oil and turpentine (not to be confused with white spirit) second layer with 100% tung-oil. Works great. The place where I glue my fletching is lacquered first (dipped) because oil and glue don't go together!