I use chef as my behind-the-scenes mechanism for managing the installs. The client is a Ruby application so I build it as a runtime dependency.
I don't use rely on the distribution Ruby because of possible conflicts with gems that would have to get installed. The goal is to be able to get everything installed and then get out of the way.
It's because I didn't want to mix in the Chef gems and dependencies with the system Ruby. I ran into some conflicts when I was initially building and testing so decided to eliminate the issue entirely.
I don't use rely on the distribution Ruby because of possible conflicts with gems that would have to get installed. The goal is to be able to get everything installed and then get out of the way.