MineOS Turnkey is just a Linux distribution with a webui. Whether you run a vanilla server or a modded server is up to you, through the choices you make in the webui and general configuration.
RCON can be enabled for Minecraft–it is done through the
server.properties file, which you can modify from within the webui (but also from outside the webui).
MineOS Turnkey comes with a firewall, which you’d want to open up to allow RCON traffic.
Answer: yes, an RCON controlled server is possible; you’d need to set it up using instructions found on the internet, same as if you were installing on Ubuntu or CentOS or anything similar.