Does rbenv work along,overrides or conflict with an apt installed ruby - and what are the implications for apt-packages that depend on ruby.
If you are using a Linux machine it is normal that even some WM depend on ruby. That should not discourage your use of rbenv and/or rvm. I personally use rvm and my colleague uses rbenv while we both have apps dependent on ruby from apt.
Conclusion: Be careful how you setup your PATH and where you put your rbenv, but there should be no collision what so ever between them because the ruby that is installed as a dependency is not even executable by you. (Just be careful to not overdo it with sudo or root user. Have a user of your own for the development part)