Are there any known African Americans who "passed" as white in  major
league baseball during the fifty years or so before Jackie Robinson
played (1947) and after the "color line" was raised keeping blacks out
of baseball? I know about blacks "passing" as cubans. And I know about
openly black players (like Moses Fleetwood) who played before the
color line was created.

Passing for Native American:

"After the advent of the independent Negro baseball team, more and
more extremely talented ball players played on the all-black teams.
Manager John J. McGraw of the Baltimore Orioles attempted to sign one
of these Negro stars by passing Charlie Grant, who had high cheekbones
and straight hair, as Charlie Tokohama, a Native American. McGraw's
ploy was, however, foiled by White Sox President Charlie Comisky. Soon
thereafter, McGraw was banned from white leagues; this act sent a
message that black players would not be accepted in the white leagues.
This message influenced a second eruption of more independent Negro
teams with notables such as the American Giants of Chicago, ABC's of
Indianapolis, and the Philadelphia Giants." [source: Negro Baseball]


Negro Baseball
http://www.wshs.fcps.k12.va.us/projects/im98/im981/spo.htm


Contraversy: Was Babe Ruth black?
http://www.blackathlete.com/baseball66.htm

According to the book Total Baseball by Thorn and Palmer (1989):

In 1887, a black man, Richard Johnson, renamed himself Dick Male and
tried to make the Syracuse team in the Southern League as a white man.
He failed to make the team.

Starting in 1911, major-league teams signed light-skinned Cubans.