hi jim
i wouldn't use the outdated .eps container format anymore, unless an old plotter or cnc cutter won't handle anything more recent.
scribus warns you about placed .pdf files because they are either rasterized or ignored by the color management. if the placed .pdf file has the right color profile (or precise colors don't really matter), you may keep it untouched, otherwise check if the export resolution for .pdf (and .eps) files is sufficient…
utnik