As far as I know, the only styles that appear in the Navigation pane are the built-in heading styles, and styles based on them.

Even if defined using the multi-level list dialog, I can't get them to show up, unless attached to heading styles or their derivatives.

You need to find the styles that are doing this (if styles were used) and create new bullet styles (or use the ones you already have). You can use the replace feature for this.