My initial estimate of the ethnic breakdown:
Northwestern European 53.5%
Jewish [or part Jewish] 35.25%
East Asian 2%
Middle Eastern 1.25%
Eastern European 1.25%
The black Forbesian is Oprah.
One of the Hispanics is John Arrilliga, son of Basque immigrants. (Do Basques consider themselves Hispanic? I know a 93-year-old Basque lady who arrived in America in the early 1920s, and still has her Basque accent.)
The other is billboard baron and Angels owner Arturo Moreno, a genuine Mexican-American from a family of 11 in Tucson.
In these estimates, Northwestern European serves as kind of a catch-all for people who don't obviously jump out at you as something else. So, maybe there's, say, a Bulgarian whose immigrant father changed his name to "Johnson" to fit in. He would get listed as Northwestern European at first glance. And "Northwestern European" doesn't recognize the fairly sizable ethnic divide between the Protestants and Catholics (Irish and more than a few Germans), who tend to have gone to separate schools.
The Jewish percentage is probably a little high because it includes some some people who are half or even just quarter Jewish by ancestry. (It may however miss some others who are part Jewish.) My preference is to allot by fraction of ancestry, but that's a lot of work.
The small number of Slavs jumps out at you. The various kinds of Slavic-Americans tend not to show up in large numbers in elites (outfielders being one exception: Musial, Yastrzemski, etc.)
RHE Notes has all 400 names and his guess at their ethnic identification, which is always interesting.
For example, after 20 years of watching the back of Larry David's head as he plays George Steinbrenner on Seinfeld, I'd assumed that the owner of the Yankees was Jewish. There's a natural tendency to assume that anybody with a Germanic-language surname who has made himself conspicuous in the media is Jewish, but that's by no means always true. Various confident-sounding individuals on the web say Steinbrenner isn't Jewish. And that's how RHE Notes lists Steinbrenner: as Northwestern European.
Steinbrenner's father's Great Lakes shipping firm was named Kinsman, perhaps after the neighborhood in Cleveland, which was a center of Cleveland's Jewish community at one point (but not at other points). His mom's name was Haley. George's upbringing seems Midwestern gentile: Culver Military Academy, Williams College, Delta Kappa Epsilon (same fraternity as the Bushes and three other Presidents), US Air Force officer, graduate assistant at Ohio State to football coach Woody Hayes, etc. Steinbrenner does have an advanced degree, but it's a Master's in P.E., which is about the least Jewish advanced degree imaginable.
So, I dunno.