It's unlikely. Your version control system provides this.
I've had a quick look at the docs and think this is the page you need.
Basically you need to add the .app to your $PATH (as the docs show in a page it links to). That's the only setup I remember doing here. The nice thing about this method is you don't have to do any arcane account setup to get something working (for local development). pg_restore and similar also become available in the terminal, since they're now on your path.
Just remember not to use sudo to install the gem (as that page suggests) because it'll mess with the permissions in your rbenv install, which should be in your user account & not need sudo (fixable with something like sudo chown -R $(whoami) ~/.rbenv)
Works fine here with rails 4 and the pg gem. Just follow the documentation.
Instead of homebrew you could use http://postgresapp.com/ which only runs when you launch the app.
It looks like either rbenv isn't installed properly, e.g. missing from your .profile or .bashrc or whatever, or it's installed but you haven't told it to use a ruby version other than your system ruby (which would install to /Library/Ruby and require sudo permissions). Install another ruby with the rbenv ruby-build plugin (also available through homebrew) and use rbenv local to switch a particular project directory to use that ruby version (it creates a .ruby-version file in the directory).