I wasn't quite able to tell from your description what is the missing piece for you: is it starting Arc inside of screen at server boot time, or restarting Racket/Mzscheme if it crashes?
I think what you want is for server boot to run screen, which runs a shell script that starts/restarts Arc, which writes its pid out to a pidfile. Does that sound about right? Each step in that process is pretty easy.
