Why not Dutch process chocolate?

Some people think that the chocolate flavor is more intense in natural cocoa than with dutch processed, which may be the reasoning behind the recommendation. So I think it's likely just the preference of the recipe author. There's no leavening involved, so no reason why you couldn't try it both ways and see which you prefer. What counts most is the quality of the cocoa, I think.

Can't see that it would harm the chemistry; I'd assume it's the author's flavor preference.