Yes, you can. And Chrubuntu has great driver support for the c720 and other popular models, but I still ran into some bugs with suspend and Wifi, so I stick with a chroot.
Crouton is a install script that uses a chroot to install Ubuntu through the shell on ChromeOS. You still need to enable developer mode, and it uses the ChromeOS kernel, but other than that it looks and feels like a "normal" Ubuntu installation.
