MC doesn't really run as a service on the Windows side (unless people use various utilities to hack it to be so), but instead has a stand-alone/linked exe that runs most of the servers. WinMC exposes some choices in the GUI on how to launch--ie. with login, server only, server and main GUI, etc.
I don't think the Mac version has this capability yet (at least, I haven't seen it), but you can achieve much the same functionality by configuring the server options the way you want them and making MC Mac a login item for your user account. It does mean that you need to be logged in, but the same thing is true on the windows side (at least without hacks).
It may be possible to find a way to trigger the behavior you're looking for by creating a custom LaunchAgent and triggering an appropriate helper app included in the MC Mac application package, but a quick poke around didn't reveal anything likely at this point.
Best,
Brad