Can a natal chart be ruled by a specific planet, in career terms at the least?
Take a native with a Cancer Midheaven (MC).
S/he may be drawn to nurturing roles. So the Moon (our life emotional centre) will rule the energies of this chart. Just as in an overall natal reading, for instance, a Pisces Rising lends to Neptune influence.
A Cancer MC career charts mean that the Moon and Cancer’s traits (caring, developing, helping, uplifting, etc.) will influence the other aspects/placements.
In my experience, this is very important when determining career potentials.
I’d propose that an MC-career ruled chart can give strong value on the competences, skills and potentials of a person. It also reflects how an individual seeks “zenith” in life, as the MC is the zenith of a chart. It literally is the highest point of the sky, within the zodiac, when a person is born.
Bill Clinton was the 42nd President of the United States (1993-2001). He has a Cancer MC, perhaps denoting liberal/Democratic politics. Or maybe seeking out the general welfare. http://www.astrotheme.com/astrology/Bill_Clinton It doesn’t necessarily mean one will enter a a “Cancerish” profession. Namely a doctor, nurse, therapist, or teacher. It does signify that “Cancerish” traits will shape how a person can shape natal potentials.
The natal chart then is a complex mix, often dictated by various influences, and with an overall theme to it.