Of course, Doc's real first name is "Harry," not "Harold," so the answer is "duh, no." Alas. But according to our friends at Baseball-Reference.com, no less than 133 men bore "Harold" as their given first or middle name into a major league ballgame. Most, it seems, went by "Hal" (including at least one hurler who might've kept Halladay from the aforementioned "best" label anyway) and four Hall of Famers.
But it's at Cooperstown that the line must be drawn ...