Can I simply make a partition on my Mac, install an OS to it, and boot from it via Startup Manner? On my Mac, can I simply create a new partition in Disk Utility, install an Operating System to it, such Arch Linux, and then boot from it by holding alt/option during boot (Startup Manager)?
I don't think so. On my Mac, even though I don't have OS X (I think its all the same though) you don't have to use option to boot into Ubuntu, but any other OS like OS X you will have to use Option to boot into it.
EDIT : Ubuntu or anything like Linux WILL NOT show up in the Option menu. It just boots straight away to Ubuntu.