Michele Pawk is breathtakingly gorgeous and she played Mama Morton. Emily could belt the crap out of that part and she's damn funny. If Pawk can be a glamorous Mama, so can Ems! :)
I see where you're going with Alice and Emily as Roxie and Velma. I can't see Alice as Velma at all, so if you were casting them together, Emily would be the obvious choice as Vel. I still see her more as a Roxie -- her character that she just played was so a "Roxie type". In fact, most of the parts she's played border more on Roxie than Velma.
I still think if freaking Melanie Griffith can headline as Roxie, Emily could play it. She can act, SING, and DANCE circles around the ho--whoa, gonna stop before I get too mean.
"You! You are the worst thing to happen to musical theatre since Andrew Lloyd Webber! And you, well, I just plain don't like you."
~Stewart Gilligan Griffin