Good question. I don’t have direct experience with either of these applied under the oil paint. My best advice is to keep the pastel and/or pencil very thin. Color pencils are waxy and if layered too heavily could act as a resist and I would be concerned that pastel might be too dusty and therefore do the same if too heavily applied. I want to add that adhesion may not be an issue at first, but could be a longer-term one that you don’t notice until the top paint film ages. A conservator would be most knowledgeable here.