I don't know what "vanilla" OSX ships with, but I've seen references to Rails pop up in logs in Console.app for my OSX Server when I was screwing with replacing their Postgres db with my own.

Er, why not? rvm was originally made for production use!

I've used rvm in production for major sites for years with no problems whatsoever, in fact I believe it is best practise. Do you have any reasons for your preference for packaged ruby?

RVM is a very impressive collection of monstrous hacks jammed into a kitchen-sink tool to achieve a set of ends that can be better met in other ways. It's worth learning enough about how the Ruby environment fits together to figure out how. It's great to get learners off the ground (assuming it works first time), but if you're doing ruby seriously then I reckon part of your education should be how to get off it as soon as possible.