I am doing an integrated league, you can read about it here:
https://forums.ootpdevelopments.com/...d.php?t=319034
Short version - I started in 19th century, and since I am not playing with minor leagues, I import every player manually. Since all the Black players import as terrible, I use Seamheads to adjust their abilities manually. For the top players I also use the Hall of Miller & Eric, they have done amazing work translating stats to major league equivalencies.
Although Negro League guys are technically in the OOTP database, they import so poorly that it barely matters. Creating them from scratch would not be much more work.