Charmed OpenStack doesn’t currently directly support running containers in OpenStack, but it looks like Cloudbase has charmed Magnum so there’s an option to use Magnum.
There is some discussion on a similar question from over a year ago that hasn’t changed much (except Gabriel’s charm moving into Cloudbase’s organization on Github).
To answer your question about feasibility of manually installing Zun on Charmed OpenStack, it would be difficult to do manually and would be better done by writing a new API charm to install Zun. The OpenStack Charms team is happy to accept community contributed OpenStack charms, a recent example that was community developed and submitted is Watcher!