Those users are supposed to be there. It's perfectly normal to find users that exist on the system that you didn't create.
I know it sounds odd, but it's true!
Those users are in place so that programs that run behind the scenes can perform tasks based on that 'users' level of permission.
www.lynda.com is an excellent place to start to learn about OS X server. The video tutorials for setting up a server right from scratch will show you step by step everything that you need to do to get up and running.
It costs 25 bucks per month, but cancel it after a month of learning os x and you've just learned the ins and outs of a server system! What a deal!!!
Hope it helps!
Graham, thanks for the reply. In a vague way I realize that background services need permissions to run.
However, I wasn't aware that those background services were normally listed in the User Accounts section of the Server application. Indeed, those background 'users' were hidden until I started messing with Webdav server.
It just seems counterintuitive to display resources related to 'hidden' services to the server admin.
Indeed. In all reality, they probably shouldn't show up there. I'm not sure why they would.
I know in Workgroup Manager, it's a preference that you can set.
In any case, you're right. It's counter intuitive. However, until a functionality problem arises, I wouldn't worry about that too much.
Just out of curiosity, have you looked at the Workgroup Manager app and seen if they display there?