Hmm.

jazz:~# emile --set-hfs
ERROR: to be bootable a partition must be of type Apple_HFS
       you can change it to Apple_HFS using "--set-hfs" argument

... Right. What was I doing again?

Index: tools/emile.c
===================================================================
--- tools/emile.c	(revision 4)
+++ tools/emile.c	(revision 5)
@@ -605,7 +605,7 @@
 		if ((action & ACTION_TEST) == 0)
 			return 6;
 	}
-	if ( (ret == 0) && (action & ACTION_SET_HFS) )
+	if ( (ret == 0) && !(action & ACTION_SET_HFS) )
 	{
 		fprintf(stderr,
 	"ERROR: to be bootable a partition must be of type Apple_HFS\n");