Actually, Norman Corwin, who Welles once said was possibly the best writer who ever worked in radio, can be considered an auxillery member of The Mercury Theatre, since he did write a couple of the Mercury Summer Theatre shows, including Jane Eyre and The Moat Farm Murder, which is probably the best of all the MST programs. I've made the change to my list of Mercury personell in the other thread.
Welles and Corwin were a good radio team. Some of the programs they collaborated on include:
Between Americans - A very good show, describing the American spirit in populist terms. Ironically, this show was delivered by Welles on Dec. 7th, the night of the Pearl Harbor bombing
The Plot to Overthrow Christmas - holiday show written, like The Night Before Christmas, entirely in verse, with Welles as Beelzebub and Ray Collins as Santa Claus.
New York - A Tapestry For Radio. A celebration of New York City's melting-pot qualities, in the days when - to paraphrase Welles - N.Y. was a genuine melting pot, not the TV-mixed cocktail it and other big cities are now. This show is on the new 6-CD set of old-time Welles radio, with excellent sound.
God and Uranium Were on Our Side