The Ly display manager doesn't seem to play very nice with OpenRC on Gentoo linux and will only display for a few seconds before being overtaken by agetty.
For anyone else who's suffering from this, an easy way to solve this is to configure Ly to start on an unused TTY instead by editing the /etc/ly/config.ini file and adding the following at the end of it (change the number to the TTY you want it to use):