I'm not sure you can manage OSX bots without using the Xcode connected to your Xcode server.
Anyway Xcode server is still very limited and you wont be able to do what you can do with Jenkins with multiple steps (ie if you use Cocoapods or if you want to deploy something at the end of the build)
If you are using Jenkins on a master server I think the best thing to do is to use your Mac server as slave via SSH to allow your Jenkins to build your iOS projects on it.