The latter. Some are alums of that MBA programme, and now return after stints in banking/consulting/PE/whatever have you, to do a different job. They also come from a diverse pool (how else can they judge a diverse applicant pool?) At least one of the Wharton adcom members, for instance, was an opera singer that toured Europe and the US.
No. Just like a HR professional cannot work for two different companies.
Also at least 2 of the adcom members at Wharton are Wharton MBA alums. They do not fit into "white female without interest in business", although some others do. Adcoms try to go for diversity too, as I mentioned.
Bear in mind that apart from reading applications, another job of the adcom is to interact with applicants. It is also a PR role.