I think this is inspired casting. As has been mentioned, Harvey literally wrote the book. He's a Broadway star, terrific in musical comedy. I saw him in the Fiddler tour and on Broadway in Hairspray. He's a good actor with great comic timing, who's able to use is, uh, unusual voice to his advantage.
Further, consider the songs he will be singing as Albin, such as (A Little More) Mascara, With You on My Arm (somewhat similar to You're Timeless to Me from Hairspray), The Best of Times, I Am What I Am. While a big soaring voice would be nice, who says that the character of Albin is necessarily a great singer with a heavenly voice? The same might be said of Tevye or Edna Turnblad. It's not like he's playing Emile de Becque.
I trust Harvey's acting ability to give powerful meaning to I Am What I Am, great comedy to Masculinity (as he did with Do You Love Me? in Fiddler) and joy to The Best of Times (as he did with You Can't Stop the Beat in Hairspray). Go Harvey!
Coach Bob knew it all along: you've got to get obsessed and stay obsessed. You have to keep passing the open windows. (John Irving, The Hotel New Hampshire)