Many minor league rosters as low as A ball are populated by players born throughout Latin America and the east Asia.

Not to mention the diversity of American born players which includes many Hispanic heritage players

The only measure that baseball would be not diverse is on the number of American born black players though that number has been steadily rising.

It is by far the most varied sport and the minors represent much of the majors.

In fact one could argue the least diverse sport is basketball which has has the the highest percentage of its players coming from the same national/ethnic breakdown as 70% of the league are black Americans.