This has now been updated. Looks like Barret Foa is out, and Melo-23 is in. From the D23 website: "Performing will be a host of special guests, including John Tartaglia (Avenue Q, Johnny and the Sprites), Ana Ortiz (Ugly Betty), Wilson Cruz (Rent, My So-Called Life), Michael Urie (Ugly Betty), Tracie Thoms (Cold Case, Rent) and Melo-23, all paying tribute to some of the most enduring tunes in the Disney canon. "
UPDATED (August 12, 2010) -
MORE STARS JOIN D23’S DESTINATION D CONCERT EVENT
‘E-TICKET: MUSIC FROM THE DISNEY PARKS’
Michael Urie (Ugly Betty), Tracie Thoms (Cold Case, Rent), and Barrett Foa (NCIS: Los Angeles) are joining a previously announced, all-star line up of performers, including Disney Legend Richard Sherman, Ana Ortiz (Ugly Betty), Wilson Cruz (My So-Called Life), and John Tartaglia (Johnny and the Sprites).
Unfortunately, I don't know who Melo-23 is.