Anything is possible, etegration.
Even striking a match on a wet cake of soap (ask for details if you're interested).
But some things are certainly easier than others.
DirectAdmin is not a multiserver control panel.
To do it you'll need to set up one copy of DA for hosting and another for Email.
Using your own login, custom skins and http tunneling between the servers you can make it fairly transparent to your users.
You'd have to create your own login system, program your own front end so your customers can make configuration updates on the server handling the service they're updating, and either reskin everything or create your own complete frontend, doing with http tunnelling (read
man curl what you can't do with APIs.
Do you want to do all that? This question is more easily answered after doing an analysis of how much time it might take you to finish and debug this certainly non-trivial project vs how much time it might take before DA offers the functionality (which is only a bit less non-trivial for them), if ever, how much it might cost you in man-hours/currency to get it done, and how much income you'd be losing.
Of course there are other control panels that do it already, but that's a story for another thread on another forum.
I'm quite happy with DA exactly the way it is
.
Jeff