In unix/linux the limitation is about opening ports with numbers lower than 1024 for listening.
I think it's the same for MAC OS X.
In fact, this limitation should only apply to non-root accounts.
As long as you are testing, you could just configure Lightstreamer for listening on a higher port number.

I can't answer about the MAC OS X LaunchDaemons insights; I hope someone else can.
The Server does nothing in particular to have this permission granted; it just relies on the system.