I guess Directadmin staff have much more important things to do, don't they? You can always disable monitoring in Directadmin and install monit from packages of your OS and configure it to do all what you need and share a config with the community, can't you?
Monit uses it's own web-gui, you are free to integrate it into Directadmin.
What could be more important?
But yes, it's on my todo list as I find the tool in DA too limited and rigid and since including Nagios within DA doesn't make sense.
I think you're right, since CB knows what's actually installed. It could add the proper scripts to monit and wipe the monitoring configs from within DA.