No. Local genital stimulation is not mandatory for reaching orgasm. The female anatomy provides for multiple erogenous zones any of which may be stimulated to reach orgasm.
In fact, it has been observed that in the event of absence or trauma to the external genitalia, existing alternate erogenous zones become more sensitive and new ones develop. Some women can reach orgasm by nipple stimulation alone. I have come across women with absent vaginas who are able to reach orgasm satisfactorily by alternate means.

In a study carried out on ritually circumcised South African women, Hanny Lightfoot Klein reports that these women had retained their orgasmic capacity in spite of the local genital mutilation.

There is not any difference between ‘clitoral orgasm’ and vaginal orgasm’. An orgasm may be more or less satisfying depending upon several Factors, but whatever be the means of stimulation, ultimately “All roads lead to Rome.”

It is not necessary that a woman should reach orgasm during intercourse. She may achieve orgasm during foreplay or after play by any method including clitoral stimulation. What is important is satisfaction, no matter how one derives it.

Difference between ‘Clitoral Orgasm’ and ‘Vaginal Orgasm’

No, there is no difference. An orgasm may be more or less satisfying depending upon several Factors, but whatever be the means of stimulation, ultimately “All roads lead to Rome.”

Can the use of a diaphragm inhibits a woman’s orgasm

The diaphragm fits into the deep portion of the vagina where there are hardly any nerve endings. Real stimulation is in the outer aspect i.e. clitoris and the surrounding area and the outer one-third of the vagina. The diaphragm in no way inhibits a woman’s orgasm.