In my experience a windows desktop is just a stripped down version of a windows server. Is it safe to say if I learn to administer windows server I can administer Desktop pretty well?
The focus is different for the desktop certifications and the server certifications. With the desktop certifications you're normally not only learning about the OS but support of the OS and the User Experience with the OS.
With the Server Certifications, this is more into the feature environment and management of what you need the Server to do and how to configure it to do it.
So can you learn the desktop experience from using server. Yes, you can personally but will it help you in supporting the end user's experience, maybe...but not guaranteed to do so if you're just relying on exam objectives to help you do so.