Well, The Color Purple (the musical) doesn't have a chance in hell of being awarded a Pulitzer. It's fun and audience-pleasing, but the book has tons of problems and the score isn't particularly distinguished. The original novel, of course, did win the Pulitzer for Literature.
The criteria for the Pulitzer for Drama are:
"For a distinguished play by an American author, preferably original in its source and dealing with American life."
So in theory it could be eligible even though it's not original, but again, it's mixed critical reception (and the Pulitzer board is usually made up of critics) all but guarantees it won't even be considered. By the way, that bit about "American life" is ignored sometimes (see I Am My Own Wife).
Other musical winners:
Of Thee I Sing
South Pacific
Fiorello!
How To Succeed
A Chorus Line
Rent
Oklahoma received a special award of merit (as did, I seem to recall, Guys and Dolls).
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
[http://margochanning.broadwayworld.com/]
"The Devil Be Hittin' Me" -- Whitney