Last week the vocal coach for the episode revealed a list of Grey's actors she worked with and it looks like Sandra Oh and Patrick Dempsey are the only cast members not on it. It remains to be seen whether or not they'll be singing, but the good news is they'll both be in the episode judging from the pic above.
Are you feeling skeptical about the episode? Don't worry, you arent't the only one:
"Ellen Pompeo [Meredith] was very much like, 'Tell me we're not going to sing and dance in the hall. This is crazy!'" recalls creator Shonda Rhimes, who dreamed up the risky concept as a love letter to fans. But after the cast's first script read-through, Rhimes says Ellen "came up to me and said, 'I never say I'm wrong, but I was wrong and I want to sing more!' She's having so much fun with it."
- Source
If you really, really want to hear Sandra Oh sing, skip to the 1:40 mark in the clip below which is from the TV show Arliss. She has a pretty good singing voice, even though she's here trying to pretend that she doesn't:
And finally, this site has a list of the songs that will be used in the episode.
