As other members have previously posted the term 'Developer' is extremely broad. Although you probably have not heard of it, there is a name for the people that come on you're server and set up plugins. They are System Admins, hint: NOT DEV. Developers design and create plugins which they then either sell off or give to a server. Developers are called Developers because they develop things. Much like the minecraft system. Plugins run in a '1.0,1.1,1.2 ect.' format. A developer develops the plugin through the stages 1 by 1. Having a real developer on your team is good but it is not their job to set up the server for you. That is a job of Admins. The difference between Sys-Admin and A regular Admin is that they have been chosen to have console access, although it will almost never be full access unless you are a Co-Owner. Developers should not be given console access. Their job is to write script or make a custom plugin for the server. They then pass these to the owner or a sys-admin who then applies it to the server.
Thank You if you actually got this far without skipping most of the text out. I tried to make a clear explanation of what a developer does and the difference it has between a sys- admin.
-GANDY