2012 article:
As of Wednesday morning, 917 players had appeared in at least one big-league game this season, according to STATS LLC. Of that group, only 39 — or 4.3 percent — were confirmed by their teams of MLB as having obtained four-year college degrees through a FOXSports.com survey of clubs. However, many got those degrees after being drafted.
Odds are low for two reasons, self-selection, the better players have left school, and age prejudice, since a senior is older, he starts out with a black mark and doesn't get the benefit of the doubt.
To me, the best bets as college seniors:
1) players coming off injuries who stayed in college to show they were healthy
2) SPs with good FBs who lack secondary pitches but are good RP prospects
3) guys who make a big jump their senior year, similar to what Kingery has done in the minors, had they been drafted as juniors the year before, that jump would have come in A ball.